Thank you for reporting. We will look at the issue as soon as possible
We already have a task related too.

These are notes for migration process.
https://ckeditor.com/docs/ckeditor5/latest/updating/ckeditor4/migration-from-ckeditor-4.html

If the process is tricky, there are also alternatives:

• Lexical https://lexical.dev/ (MIT license)
• TinyMCE https://github.com/tinymce/tinymce (GPLv2 license)

I guess a markdown editor is not a choice, because of that situations in which the survey administrator injected javascript code such as jquery.