MigrateDrupalUiRouteSubscriber.php

<?php

namespace Drupal\migrate_drupal_ui\Routing;

use Drupal\Core\Routing\RouteSubscriberBase;
use Symfony\Component\Routing\RouteCollection;

/**
 * Sets the controller for Migrate Message route.
 */
class MigrateDrupalUiRouteSubscriber extends RouteSubscriberBase {
    
    /**
     * {@inheritdoc}
     */
    protected function alterRoutes(RouteCollection $collection) {
        $route = $collection->get('migrate.messages');
        if ($route) {
            $route->setDefault('_controller', '\\Drupal\\migrate_drupal_ui\\Controller\\MigrateMessageController::overview');
        }
    }

}