Item format custom HTML is not valid.

Can you confirm that the date format machine name → Y年 is the cause? If so, how did you enter Y年 as a date format machine name?

When investigating webform/src/Plugin/WebformElement/DateBase.php:183, we found that it directly uses DateFormat::load('Y年') for query. In drupal, the format of id has requirements that do not allow the use of '年'. This kind of character.

I found two related questions.
https://www.drupal.org/project/drupal/issues/3415478 🐛 \Drupal::entityTypeManager()->getStorage('user_role')->load() can't load non-english string Closed: won't fix
https://www.drupal.org/project/webform/issues/3415445 🐛 Search Chinese in /admin/structure/webform cause error: Illegal mix of collations Closed: duplicate

Please put the patch into an issue fork and merge request.

We need to standardize our approach to special character in config entity id.

The MR also updates 🐛 \Drupal::entityTypeManager()->getStorage('user_role')->load() can't load non-english string Closed: won't fix to use mb_convert_encoding($keys, 'ASCII', 'UTF-8') which feels easier to understand than iconv('UTF-8', 'ASCII//TRANSLIT', $keys) and both statement accomplish similar goals.

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