Compatibility with ckeditor5

Since the "Table of contents" from Ckeditor5 is now a premium feature, I think we can not port this functonality.
https://ckeditor.com/docs/ckeditor5/latest/features/table-of-contents.html

To be able to use "Table of contents" in Ckeditor5 you need to have the paid plan and you can use this Drupal module with that:
https://www.drupal.org/project/ckeditor5_premium_features →