Doesn't work in layout builder

If you place a field using Layout Builder and try to give it a delimiter, your setting is ignored. This is related to #3061187: #view_mode is always "_custom" in HOOK_preprocess_field() with layout_builder enabled → .

A fix here looks like this:

  $view_mode = $element['#view_mode'];

  // Add a check for Layout Builder alternative settings.
  if ($view_mode == '_custom') {
    $view_mode = $element['#third_party_settings']['layout_builder']['view_mode'];
  }

Note that this fix will only work in Drupal 8.8+, in earlier versions it's just broken.