Use this code:

function change_user_role_after_category_purchase($order_id) {
    // Get the order object
    $order = wc_get_order($order_id);

    // Get the user ID of the customer
    $user_id = $order->get_user_id();

    // Define the target product category
    $target_category = 'example-category'; // Replace with your category slug

    // Check if the order contains products from the target category
    foreach ($order->get_items() as $item_id => $item) {
        $product_id = $item->get_product_id();

        if (has_term($target_category, 'product_cat', $product_id)) {
            // Change the user role
            $user = new WP_User($user_id);
            $user->set_role('new_role'); // Replace 'new_role' with your desired role slug

            // Exit the loop after finding a match
            break;
        }
    }
}

add_action('woocommerce_order_status_completed', 'change_user_role_after_category_purchase');

• Replace the placeholders:

  • Replace example-category with the slug of your target product category.
  • Replace new_role with the role you want to assign (e.g., subscriber, customer, editor, etc.).

• Add the code:

  • Navigate to your WordPress Dashboard.
  • Go to Appearance > Theme File Editor.
  • Open the functions.php file of your active theme and paste the code at the bottom.

• Test the functionality:

  • Make a test purchase from the target category and ensure the user role is updated after the purchase is marked as "Completed."

You can also use the plugin Automatic User Roles Switcher for WooCommerce (although I had a conflict with it):

https://woocommerce.com/products/automatic-user-roles-switcher/