Hi,
so @mflorea would probably give you better answers, but short answer is no we don’t use CKEditor 4 - LTS but latest version of CKEditor which reached end of life support.
You can see a big discussion on Hi! Have any plan to use ckeditor 5 in XWiki? about the difficulty to migrate to CKEditor 5. We’re actively working on finding an alternative, you can check Choice of editor, we’re using Cristal development as a playground to also take a decision for the future editor in XWiki.
Hope that answers your questions.