How to display the rendered entity of the user ?

You need to add an entry to hook_token_info for user-render.
In hook_tokens something like this:

case 'user-render':
  $entity = $message->getOwner();
  $view_builder = \Drupal::entityTypeManager()->getViewBuilder($entity->getEntityTypeId());
  $message_view = $view_builder->view($entity, 'teaser');
  $replacements[$original] = \Drupal::service('renderer')->renderRoot($message_view);
  break;

Automatically closed - issue fixed for 2 weeks with no activity.