Is it possible to load a webform that is using a specific custom handler?
You can use the next code:
$webforms = \Drupal::entityTypeManager()-&gt;getStorage('webform')-&gt;loadMultiple();
  foreach ($webforms as $webform) {
    foreach ($webform-&gt;getHandlers() as $handler) {
      if ($handler-&gt;getPluginId() == 'your_custom_handler') {
        // do your logic.
        break;
      }
    }
  }