In https://github.com/backdrop/backdrop-issues/issues/1725, we encountered an issue where it would be desirable to load the admin theme dialog styling rather than the front-end dialog styling. Take this example of deleting a block from the front-end:

As this is an admin-action, it may make sense to have this be styled in the admin theme.
GitHub Issue #:
2659
Recent comments
Yes, you can use TinyMCE on some content and CKEditor5 in others. There is no problem having both enabled on a system.
Specific tags to work in CKEditor 5
Thank you both for your suggestions. Yeah, I'll give TinyMCE a try... better than trying to fight that behemoth CKEditor 5. The TinyMCE page says it can "co-exist with CKEditor" which is...
Specific tags to work in CKEditor 5
The specific tags I need are "<ruby>" and "<rt>" Wow, yeah, that's a pain with CKEditor5. A custom plugin, for sure, but no clue, what the code has to look like...
Specific tags to work in CKEditor 5