It is not possible to override the system 404 page on D10.2+

This piece of code is no longer needed (these templates are suggested by default now):

// Adds template suggestions for 40x pages.
  $http_error_suggestions = [
    'system.403' => 'page__403',
    'system.404' => 'page__404',
  ];
  $route_name = \Drupal::routeMatch()->getRouteName();
  if (isset($http_error_suggestions[$route_name])) {
    $suggestions[] = $http_error_suggestions[$route_name];
  }

@andre.bonon is there a harm in keeping it for now? I think many folks using this may still be using Drupal 10.0.x.

Is openy_carnation still compatible with 10.0.x?

Regardless of what we decide, I've pushed a fix to ensure the exception is an instance of NotFoundHttpException, because in some cases the Exception might be of another type and the response doesn't have a status code.

@andre.bonon yes, openy_carnation should stay compatible with 10.0.x.

This change makes sense and I think it helps to make the code more readable as well. Thank you.