The steps to workaround this problem are in the first comment of this topic: RT 5 wysiwyg editor not working in Firefox 148+
To fix this in our installation, I copied the ckeditor.min.js file (located at “/usr/share/request-tracker5/static/RichText/” on Debian) to the override directory (“/usr/local/share/request-tracker5/static/RichText/” on Debian) and patching it to have version=”4.DEV” instead.
After clearing the mason cache and restarting the editor was working again.
I didn’t need to do this because I’m not using Debian.
If you need help on how to do this, better ask in the other topic.