diff --git a/AI-AGENTS.md b/AI-AGENTS.md
index b5248b3e398..bda2eafdd1a 100644
--- a/AI-AGENTS.md
+++ b/AI-AGENTS.md
@@ -30,9 +30,10 @@ Discourse is large with long history. Understand context before changes.
 - Members: specify `@type`
 
 ## Testing
+- Do not write unnecessary comments in tests, every single assertion doesn't need a comment
 - Don't test functionality handled by other classes/components
 - Don't write obvious tests
-- Ruby: use `fab!()` over `let()`, system tests for UI (`spec/system`), page objects (`spec/system/page_objects`)
+- Ruby: use `fab!()` over `let()`, system tests for UI (`spec/system`), use page objects for system spec finders (`spec/system/page_objects`)
 
 ### Commands
 ```bash
diff --git a/app/assets/javascripts/admin/addon/components/site-setting.gjs b/app/assets/javascripts/admin/addon/components/site-setting.gjs
index 98a1df33042..b42505d72aa 100644
--- a/app/assets/javascripts/admin/addon/components/site-setting.gjs
+++ b/app/assets/javascripts/admin/addon/components/site-setting.gjs
@@ -12,9 +12,11 @@ import { isNone } from "@ember/utils";
 import { and } from "truth-helpers";
 import DButton from "discourse/components/d-button";
 import JsonSchemaEditorModal from "discourse/components/modal/json-schema-editor";
+import basePath from "discourse/helpers/base-path";
 import icon from "discourse/helpers/d-icon";
 import { bind } from "discourse/lib/decorators";
 import { deepEqual } from "discourse/lib/object";
+import { sanitize } from "discourse/lib/text";
 import { splitString } from "discourse/lib/utilities";
 import { i18n } from "discourse-i18n";
 import SettingValidationMessage from "admin/components/setting-validation-message";
@@ -55,6 +57,7 @@ export default class SiteSettingComponent extends Component {
   @service router;
   @service siteSettingChangeTracker;
   @service messageBus;
+  @service site;
 
   @tracked isSecret = null;
   @tracked status = null;
@@ -92,6 +95,10 @@ export default class SiteSettingComponent extends Component {
     );
   }
 
+  get defaultTheme() {
+    return this.site.user_themes.find((theme) => theme.default);
+  }
+
   @bind
   async onMessage(membership) {
     this.status = membership.status;
@@ -131,6 +138,20 @@ export default class SiteSettingComponent extends Component {
     return this.componentType !== "bool";
   }
 
+  get showThemeSiteSettingWarning() {
+    return this.setting.themeable;
+  }
+
+  get themeSiteSettingWarningText() {
+    return htmlSafe(
+      i18n("admin.theme_site_settings.site_setting_warning", {
+        basePath,
+        defaultThemeName: sanitize(this.defaultTheme.name),
+        defaultThemeId: this.defaultTheme.theme_id,
+      })
+    );
+  }
+
   get dirty() {
     let bufferVal = this.buffered.get("value");
     let settingVal = this.setting?.value;
@@ -266,6 +287,10 @@ export default class SiteSettingComponent extends Component {
   }
 
   get canUpdate() {
+    if (this.setting.themeable) {
+      return false;
+    }
+
     if (!this.status || this.status === "completed") {
       return true;
     } else {
@@ -429,6 +454,7 @@ export default class SiteSettingComponent extends Component {
         {{else}}
           <this.resolvedComponent
             {{on "keydown" this._handleKeydown}}
+            @disabled={{this.setting.themeable}}
             @setting={{this.setting}}
             @value={{this.buffered.value}}
             @preview={{this.preview}}
@@ -444,6 +470,14 @@ export default class SiteSettingComponent extends Component {
             <Description @description={{this.setting.description}} />
             <JobStatus @status={{this.status}} @progress={{this.progress}} />
           {{/if}}
+          {{#if this.showThemeSiteSettingWarning}}
+            <div class="setting-theme-warning">
+              <p class="setting-theme-warning__text">
+                {{icon "paintbrush"}}
+                {{this.themeSiteSettingWarningText}}
+              </p>
+            </div>
+          {{/if}}
         {{/if}}
       </div>
 
diff --git a/app/assets/javascripts/admin/addon/components/site-settings/bool.gjs b/app/assets/javascripts/admin/addon/components/site-settings/bool.gjs
index e0249333e12..b46f60b1911 100644
--- a/app/assets/javascripts/admin/addon/components/site-settings/bool.gjs
+++ b/app/assets/javascripts/admin/addon/components/site-settings/bool.gjs
@@ -26,6 +26,7 @@ export default class Bool extends Component {
         {{on "input" this.onToggle}}
         type="checkbox"
         checked={{this.enabled}}
+        disabled={{@disabled}}
       />
       <span>{{htmlSafe @setting.description}}</span>
     </label>
diff --git a/app/assets/javascripts/admin/addon/components/site-settings/enum.gjs b/app/assets/javascripts/admin/addon/components/site-settings/enum.gjs
index f39ae6edebf..770b8169dae 100644
--- a/app/assets/javascripts/admin/addon/components/site-settings/enum.gjs
+++ b/app/assets/javascripts/admin/addon/components/site-settings/enum.gjs
@@ -11,7 +11,11 @@ export default class Enum extends Component {
       @onChange={{fn (mut this.value)}}
       @valueProperty={{this.setting.computedValueProperty}}
       @nameProperty={{this.setting.computedNameProperty}}
-      @options={{hash castInteger=true allowAny=this.setting.allowsNone}}
+      @options={{hash
+        castInteger=true
+        allowAny=this.setting.allowsNone
+        disabled=@disabled
+      }}
     />
 
     {{this.preview}}
diff --git a/app/assets/javascripts/admin/addon/components/site-settings/host-list.gjs b/app/assets/javascripts/admin/addon/components/site-settings/host-list.gjs
index 7807220af25..fd63cee3356 100644
--- a/app/assets/javascripts/admin/addon/components/site-settings/host-list.gjs
+++ b/app/assets/javascripts/admin/addon/components/site-settings/host-list.gjs
@@ -28,7 +28,7 @@ export default class HostList extends Component {
       @settingName={{this.setting.setting}}
       @choices={{this.settingValue}}
       @onChange={{this.onChange}}
-      @options={{hash allowAny=this.allowAny}}
+      @options={{hash allowAny=this.allowAny disabled=@disabled}}
     />
   </template>
 }
diff --git a/app/assets/javascripts/admin/addon/components/site-settings/integer.gjs b/app/assets/javascripts/admin/addon/components/site-settings/integer.gjs
index 211c516b4e4..292e477438f 100644
--- a/app/assets/javascripts/admin/addon/components/site-settings/integer.gjs
+++ b/app/assets/javascripts/admin/addon/components/site-settings/integer.gjs
@@ -34,6 +34,7 @@ export default class SiteSettingsInteger extends Component {
       max={{if @setting.max @setting.max null}}
       class="input-setting-integer"
       step="1"
+      disabled={{@disabled}}
     />
   </template>
 }
diff --git a/app/assets/javascripts/admin/addon/components/site-settings/list.gjs b/app/assets/javascripts/admin/addon/components/site-settings/list.gjs
index bfedb2e3566..9a61e8332f8 100644
--- a/app/assets/javascripts/admin/addon/components/site-settings/list.gjs
+++ b/app/assets/javascripts/admin/addon/components/site-settings/list.gjs
@@ -8,6 +8,7 @@ export default class List extends Component {
       @values={{this.value}}
       @inputDelimiter="|"
       @choices={{this.setting.choices}}
+      @disabled={{@disabled}}
     />
   </template>
 }
diff --git a/app/assets/javascripts/admin/addon/components/site-settings/string.gjs b/app/assets/javascripts/admin/addon/components/site-settings/string.gjs
index 1396355e5ed..0d5a0087508 100644
--- a/app/assets/javascripts/admin/addon/components/site-settings/string.gjs
+++ b/app/assets/javascripts/admin/addon/components/site-settings/string.gjs
@@ -5,16 +5,25 @@ import TextField from "discourse/components/text-field";
 export default class String extends Component {
   <template>
     {{#if this.setting.textarea}}
-      <Textarea @value={{this.value}} class="input-setting-textarea" />
+      <Textarea
+        @value={{this.value}}
+        class="input-setting-textarea"
+        @disabled={{@disabled}}
+      />
     {{else if this.isSecret}}
       <Input
         @type="password"
         @value={{this.value}}
         class="input-setting-string"
         autocomplete="new-password"
+        @disabled={{@disabled}}
       />
     {{else}}
-      <TextField @value={{this.value}} @classNames="input-setting-string" />
+      <TextField
+        @value={{this.value}}
+        @classNames="input-setting-string"
+        @disabled={{@disabled}}
+      />
     {{/if}}
   </template>
 }
diff --git a/app/assets/javascripts/admin/addon/components/site-settings/tag-group-list.gjs b/app/assets/javascripts/admin/addon/components/site-settings/tag-group-list.gjs
index 0dde8d24190..6886b16533a 100644
--- a/app/assets/javascripts/admin/addon/components/site-settings/tag-group-list.gjs
+++ b/app/assets/javascripts/admin/addon/components/site-settings/tag-group-list.gjs
@@ -22,6 +22,7 @@ export default class TagGroupList extends Component {
       @onChange={{this.onTagGroupChange}}
       @options={{hash
         filterPlaceholder="category.required_tag_group.placeholder"
+        disabled=@disabled
       }}
     />
   </template>
diff --git a/app/assets/javascripts/admin/addon/components/site-settings/tag-list.gjs b/app/assets/javascripts/admin/addon/components/site-settings/tag-list.gjs
index 5fb2afbed57..4116a6446e1 100644
--- a/app/assets/javascripts/admin/addon/components/site-settings/tag-list.gjs
+++ b/app/assets/javascripts/admin/addon/components/site-settings/tag-list.gjs
@@ -22,7 +22,7 @@ export default class TagList extends Component {
       @onChange={{this.changeSelectedTags}}
       @everyTag={{true}}
       @unlimitedTagCount={{true}}
-      @options={{hash allowAny=false}}
+      @options={{hash allowAny=false disabled=@disabled}}
     />
   </template>
 }
diff --git a/app/assets/javascripts/admin/addon/components/site-settings/upload.gjs b/app/assets/javascripts/admin/addon/components/site-settings/upload.gjs
index 6890de204f6..926f0516d41 100644
--- a/app/assets/javascripts/admin/addon/components/site-settings/upload.gjs
+++ b/app/assets/javascripts/admin/addon/components/site-settings/upload.gjs
@@ -26,6 +26,7 @@ export default class Upload extends Component {
       @additionalParams={{hash for_site_setting=true}}
       @type="site_setting"
       @id={{concat "site-setting-image-uploader-" this.setting.setting}}
+      @disabled={{@disabled}}
     />
   </template>
 }
diff --git a/app/assets/javascripts/admin/addon/components/site-settings/uploaded-image-list.gjs b/app/assets/javascripts/admin/addon/components/site-settings/uploaded-image-list.gjs
index 63a50934057..98f6a473503 100644
--- a/app/assets/javascripts/admin/addon/components/site-settings/uploaded-image-list.gjs
+++ b/app/assets/javascripts/admin/addon/components/site-settings/uploaded-image-list.gjs
@@ -27,6 +27,7 @@ export default class UploadedImageList extends Component {
         this.showUploadModal
         (hash value=this.value setting=this.setting)
       }}
+      @disabled={{@disabled}}
     />
   </template>
 }
diff --git a/app/assets/javascripts/admin/addon/components/site-settings/url-list.gjs b/app/assets/javascripts/admin/addon/components/site-settings/url-list.gjs
index e51bef670b5..4bbae9e2994 100644
--- a/app/assets/javascripts/admin/addon/components/site-settings/url-list.gjs
+++ b/app/assets/javascripts/admin/addon/components/site-settings/url-list.gjs
@@ -4,6 +4,10 @@ import ValueList from "admin/components/value-list";
 
 export default class UrlList extends Component {
   <template>
-    <ValueList @values={{this.value}} @addKey="admin.site_settings.add_url" />
+    <ValueList
+      @disabled={{@disabled}}
+      @values={{this.value}}
+      @addKey="admin.site_settings.add_url"
+    />
   </template>
 }
diff --git a/app/assets/javascripts/admin/addon/components/site-settings/value-list.gjs b/app/assets/javascripts/admin/addon/components/site-settings/value-list.gjs
index 35819d0b5db..092fd645872 100644
--- a/app/assets/javascripts/admin/addon/components/site-settings/value-list.gjs
+++ b/app/assets/javascripts/admin/addon/components/site-settings/value-list.gjs
@@ -3,5 +3,7 @@ import Component from "@ember/component";
 import ValueList from "admin/components/value-list";
 
 export default class SiteSettingValueList extends Component {
-  <template><ValueList @values={{this.value}} /></template>
+  <template>
+    <ValueList @disabled={{@disabled}} @values={{this.value}} />
+  </template>
 }
diff --git a/app/assets/javascripts/admin/addon/components/value-list.gjs b/app/assets/javascripts/admin/addon/components/value-list.gjs
index 79c7711b7e8..dfdf77fba8b 100644
--- a/app/assets/javascripts/admin/addon/components/value-list.gjs
+++ b/app/assets/javascripts/admin/addon/components/value-list.gjs
@@ -187,7 +187,7 @@ export default class ValueList extends Component {
       @value={{this.newValue}}
       @content={{this.filteredChoices}}
       @onChange={{this.selectChoice}}
-      @options={{hash allowAny=true none=this.noneKey}}
+      @options={{hash allowAny=true none=this.noneKey disabled=@disabled}}
     />
   </template>
 }
diff --git a/app/assets/javascripts/discourse/tests/integration/components/site-setting-test.gjs b/app/assets/javascripts/discourse/tests/integration/components/site-setting-test.gjs
index 7495c6a38d4..e0f2af6ce46 100644
--- a/app/assets/javascripts/discourse/tests/integration/components/site-setting-test.gjs
+++ b/app/assets/javascripts/discourse/tests/integration/components/site-setting-test.gjs
@@ -358,6 +358,83 @@ module("Integration | Component | SiteSetting", function (hooks) {
   });
 });
 
+module(
+  "Integration | Component | SiteSetting | Themeable Settings",
+  function (hooks) {
+    setupRenderingTest(hooks);
+
+    test("disables input for themeable site settings", async function (assert) {
+      const self = this;
+
+      this.site = this.container.lookup("service:site");
+      this.site.set("user_themes", [
+        { theme_id: 5, default: true, name: "Default Theme" },
+      ]);
+
+      this.set(
+        "setting",
+        SiteSetting.create({
+          setting: "test_themeable_setting",
+          value: "test value",
+          type: "string",
+          themeable: true,
+        })
+      );
+
+      await render(
+        <template><SiteSettingComponent @setting={{self.setting}} /></template>
+      );
+
+      assert.dom(".input-setting-string").hasAttribute("disabled", "");
+      assert
+        .dom(".setting-controls__ok")
+        .doesNotExist("save button is not shown");
+    });
+
+    test("shows warning text for themeable site settings", async function (assert) {
+      const self = this;
+
+      this.site = this.container.lookup("service:site");
+      this.site.set("user_themes", [
+        { theme_id: 5, default: true, name: "Default Theme" },
+      ]);
+
+      this.set(
+        "setting",
+        SiteSetting.create({
+          setting: "test_themeable_setting",
+          value: "test value",
+          type: "string",
+          themeable: true,
+        })
+      );
+
+      await render(
+        <template><SiteSettingComponent @setting={{self.setting}} /></template>
+      );
+
+      assert
+        .dom(".setting-theme-warning")
+        .exists("warning wrapper is displayed");
+
+      assert
+        .dom(".setting-theme-warning__text")
+        .exists("warning text element is displayed");
+
+      const expectedText = i18n(
+        "admin.theme_site_settings.site_setting_warning",
+        {
+          basePath: "",
+          defaultThemeName: "Default Theme",
+          defaultThemeId: 5,
+        }
+      );
+
+      assert.dom(".setting-theme-warning__text").includesHtml(expectedText);
+    });
+  }
+);
+
 module(
   "Integration | Component | SiteSetting | file_size_restriction type",
   function (hooks) {
diff --git a/app/assets/stylesheets/admin/settings.scss b/app/assets/stylesheets/admin/settings.scss
index 9a758cad273..86c4c6fbf87 100644
--- a/app/assets/stylesheets/admin/settings.scss
+++ b/app/assets/stylesheets/admin/settings.scss
@@ -73,6 +73,16 @@
       }
     }
 
+    .setting-theme-warning {
+      font-size: var(--font-down-1);
+      color: var(--primary-medium);
+
+      .d-icon {
+        font-size: var(--font-down-1);
+        vertical-align: baseline;
+      }
+    }
+
     .setting-controls {
       float: left;
     }
diff --git a/app/controllers/admin/site_settings_controller.rb b/app/controllers/admin/site_settings_controller.rb
index 832f2d13ce1..6a98921f66f 100644
--- a/app/controllers/admin/site_settings_controller.rb
+++ b/app/controllers/admin/site_settings_controller.rb
@@ -14,6 +14,8 @@ class Admin::SiteSettingsController < Admin::AdminController
           filter_plugin: params[:plugin],
           filter_names: params[:names],
         ),
+      default_theme:
+        BasicThemeSerializer.new(Theme.find_default, scope: guardian, root: false).as_json,
     )
   end
 
diff --git a/config/locales/client.en.yml b/config/locales/client.en.yml
index f9cecb59d09..217b4ebcdae 100644
--- a/config/locales/client.en.yml
+++ b/config/locales/client.en.yml
@@ -5964,6 +5964,7 @@ en:
         help: "The theme you are currently using is <a href='%{basePath}/admin/customize/themes/%{currentThemeId}'>%{currentTheme}</a>. Go to the <a href='%{basePath}/admin/customize/themes/%{currentThemeId}'>theme config page</a> to alter theme site settings, or click on a linked theme in the table below to edit its settings."
         filter: "Filter theme site settings by setting name, description, or theme name..."
         filter_no_results: "No theme site settings match your filter"
+        site_setting_warning: 'This setting is managed by the default theme for your site (%{defaultThemeName}). You can modify it from <a href="%{basePath}/admin/customize/themes/%{defaultThemeId}">the theme''s edit page</a>.'
 
       search:
         modal_title: "Search everything in admin"
diff --git a/config/locales/server.en.yml b/config/locales/server.en.yml
index 6a10b8eed23..290e9e4045d 100644
--- a/config/locales/server.en.yml
+++ b/config/locales/server.en.yml
@@ -2761,7 +2761,6 @@ en:
     default_composition_mode: "Set the default mode for your community's composer. Rich text mode provides a more modern, familiar writing experience for most users, while Markdown mode may be suitable for more technical audiences. Members can use a toggle in the composer toolbar to switch between modes."
     viewport_based_mobile_mode: "EXPERIMENTAL: Disable the user-agent-based mobile/desktop modes and use viewport width instead."
     reviewable_ui_refresh: "Groups that can use the experimental new UI in the review queue."
-
     content_localization_enabled: "Displays localized content for users based on their browser or user language preferences. Such content may include categories, tags, posts, and topics. Supported locales are set in 'content localization supported locales'."
     content_localization_supported_locales: "List of supported locales that user content can be translated to. Requires 'content localization enabled'."
     content_localization_allowed_groups: "Groups allowed to update localized content. Requires 'content localization enabled'."
diff --git a/lib/site_setting_extension.rb b/lib/site_setting_extension.rb
index 26740f97219..1c9787f83fa 100644
--- a/lib/site_setting_extension.rb
+++ b/lib/site_setting_extension.rb
@@ -339,16 +339,16 @@ module SiteSettingExtension
           true
         end
       end
-      .reject do |setting_name, _|
-        # Do not show themeable site settings all_settings list or in the UI, they
-        # are managed separately via the ThemeSiteSetting model.
-        themeable[setting_name]
-      end
       .map do |s, v|
         type_hash = type_supervisor.type_hash(s)
         default = defaults.get(s, default_locale).to_s
 
-        value = public_send(s)
+        if themeable[s]
+          value = public_send(s, { theme_id: SiteSetting.default_theme_id })
+        else
+          value = public_send(s)
+        end
+
         value = value.map(&:to_s).join("|") if type_hash[:type].to_s == "uploaded_image_list"
 
         if type_hash[:type].to_s == "upload" && default.to_i < Upload::SEEDED_ID_THRESHOLD
diff --git a/spec/system/admin_config_theme_site_settings_spec.rb b/spec/system/admin_config_theme_site_settings_spec.rb
index 90f0f205e92..c54a9e0c49a 100644
--- a/spec/system/admin_config_theme_site_settings_spec.rb
+++ b/spec/system/admin_config_theme_site_settings_spec.rb
@@ -44,4 +44,20 @@ describe "Admin Theme Site Settings", type: :system do
       "search_field",
     )
   end
+
+  describe "all site setting list" do
+    fab!(:default_theme) { Theme.find_default }
+    let(:site_settings_page) { PageObjects::Pages::AdminSiteSettings.new }
+
+    it "shows warning and disabled state for themeable site settings" do
+      site_settings_page.visit("enable_welcome_banner")
+
+      expect(site_settings_page).to have_disabled_input("enable_welcome_banner")
+      expect(site_settings_page).to have_theme_warning(
+        "enable_welcome_banner",
+        default_theme.name,
+        default_theme.id,
+      )
+    end
+  end
 end
diff --git a/spec/system/page_objects/pages/admin_site_settings.rb b/spec/system/page_objects/pages/admin_site_settings.rb
index 92865892497..c65700afdb2 100644
--- a/spec/system/page_objects/pages/admin_site_settings.rb
+++ b/spec/system/page_objects/pages/admin_site_settings.rb
@@ -141,6 +141,17 @@ module PageObjects
         setting = find_setting(setting_name)
         setting.find(".setting-value .validation-error").text
       end
+
+      def has_theme_warning?(setting_name, theme_name, theme_id)
+        find_setting(setting_name).find(".setting-theme-warning__text").has_text?(theme_name) &&
+          find_setting(setting_name).find(".setting-theme-warning__text").has_link?(
+            href: "/admin/customize/themes/#{theme_id}",
+          )
+      end
+
+      def has_disabled_input?(setting_name)
+        find_setting(setting_name).has_css?("input[disabled]")
+      end
     end
   end
 end