Code-Snippets-Functions/Execute a function on a child site/WooCommerce/disable-add-to-cart-backorder-product.txt

add_filter('woocommerce_is_purchasable', 'disable_add_to_cart', 10, 2);

function disable_add_to_cart($purchasable, $product) {
    if ($product->is_on_backorder(1))
        $purchasable = false;
    return $purchasable;
}