The first place to start looking at is the vendor directory and see if you can find ckeditor under vendor/egroupware path. Maybe something went wrong while installing composer packages. We have egroupware specific ckeditor package in here
Second, make sure that there's no git checkout of ckeditor in your .mrconfig file anymore. The Ckediotr library no longer gets included in api/js therefore there should be no binding path of ckeditor.js to the api/js directory anymore.
Hope this helps to get your ckeditor back.
EGroupware GmbH [www.egroupware.org]
Handelsregister HRB Kaiserslautern 3587
Geschäftsführer Birgit und Ralf Becker
Leibnizstr. 17, 67663 Kaiserslautern, Germany
Telefon +49 631 31657-0 e