loadBundleDescriptions example

      // Filter out the bundles the user doesn't have access to.       $access_control_handler = $this->entityTypeManager->getAccessControlHandler($entity_type_id);
      foreach ($bundles as $bundle_name => $bundle_info) {
        $access = $access_control_handler->createAccess($bundle_name, NULL, [], TRUE);
        if (!$access->isAllowed()) {
          unset($bundles[$bundle_name]);
        }
        $this->renderer->addCacheableDependency($build, $access);
      }
      // Add descriptions from the bundle entities.       $bundles = $this->loadBundleDescriptions($bundles, $bundle_entity_type);
    }
    else {
      $bundle_argument = $bundle_key;
    }

    $form_route_name = 'entity.' . $entity_type_id . '.add_form';
    // Redirect if there's only one bundle available.     if (count($bundles) == 1) {
      $bundle_names = array_keys($bundles);
      $bundle_name = reset($bundle_names);
      $parameters = $this->routeMatch->getRawParameters()->all();