Définir une route qui appelle la méthode content du contrôleur FirstController.

mymodule/mymodule.routing.yml

mymodule.content:
  path: '/mymodule'
  defaults:
    _controller: '\Drupal\mymodule\Controller\FirstController::content'
    _title: 'My First page and Menu Item'
  requirements:
    _permission: 'access content'

La méthode renvoie un Render Array.

mymodule/src/Controller/FirstController.php

<?php
namespace Drupal\mymodule\Controller;
 
use Drupal\Core\Controller\ControllerBase;
 
class FirstController extends ControllerBase {
 
  public function content() {
    return array(
      '#type' => 'markup',
      '#markup' => t('This is my menu linked custom page'),
    );
  }
 
}