Drupal 11.1 removes unintended usage of hook_library_info_build() by themes.

Unfortunately, this change will likely need to be rolled manually by everyone currently using any subtheme generated prior to us fixing this since those subthemes will use the incorrect hook.

For those looking for a quick fix using a generated subtheme:

1. Replace function HOOK_library_info_build() { with function HOOK_library_info_alter(&$libraries, $extension) {.
2. Remove the line that says $libraries = [];
3. Remove the line that says return $libraries;

That should get your layout and extension libraries working again.

Thanks @ I fixed boostrap_italia theme with your solution https://www.drupal.org/project/bootstrap_italia/issues/3501035 🐛 Drupal 11.1 breaks theme Active