Problems creating a custom blank page with my custom module
You can output the html of one twig only in a symfony response:

use Symfony\Component\HttpFoundation\Response;

public function my_page_controller() {

  $build = array(
    'page' =&gt; array(
      '#theme' =&gt; 'videoPage',
      '#content' =&gt; $content,
    ),
  );
  $html = \Drupal::service('renderer')-&gt;renderRoot($build);
  $response = new Response();
  $response-&gt;setContent($html);

  return $response;
}