The controller must return a "Symfony\Component\HttpFoundation\Response" object but it returned null. Did you forget to add a return statement somewhere in your controller?

Problem:

Symfony\Component\HttpKernel\Exception\ControllerDoesNotReturnResponseException: The controller must return a "Symfony\Component\HttpFoundation\Response" object but it returned null. Did you forget to add a return statement somewhere in your controller? in () (Line 98 in /var/www/web/core/lib/Drupal/Core/EventSubscriber/EarlyRenderingControllerWrapperSubscriber.php).

Solution (in Controller):

<?php

namespace Drupal\my_module2024\Controller;

use Drupal\Core\Controller\ControllerBase;
use \Symfony\Component\HttpFoundation\Response;
use Symfony\Component\HttpFoundation\RedirectResponse;
use Drupal\Core\Url;
use Drupal\Core\Link;
use Drupal\Core\Render\Markup;
use Drupal\Core\Access\AccessResult;

class myClass123 extends ControllerBase {

    public function my_main_func( )
    {
            // ... some code
            $response = new RedirectResponse( $link, 302);
            $response->send();

            return $response;
            
    }
}

Important:  return $response;