Support Filter : Limit allowed HTML tags and correct faulty HTML

fn is from the 3x branch, dud you mean that? 4x should work fine (but with the new element after upgrade path, not fn). Detail in 🌱 Roadmap to stable 4x branch Active - I still need to update the module homepage sorry.

For 3x perhaps try changing the order of filter processing and see if that helps.

I had tested it separately with FN and ckeditor 5 button. It's ok if [FN] is valid for v.3, but it did not work with Ckeditor5 Footnotes button.
Now, I have tested Version 4 alpha3 and dev version, again.
It still only allows me if I deactive the filter of "Limit allowed HTML tags and correct faulty HTML". Check screenshots, please.

Can you show the filter order you have set up in a further screenshot? You do need to make sure Footnotes Filter is applied before Limit HTML is applied

Thanks.
Now, it's ok. It works.

Great to hear! I have updated the module homepage with more installation instructions.