EDIT: Solved. The helpful comments lead me to this thread: https://www.reddit.com/r/Calibre/comments/1c2ryfz/2024_guide_to_dedrm_kindle_books/
Paying attention to the version numbers worked like a charm. Thanks to everyone!
I am looking for #fediHelp. I intend to move my #ebook consumption away from #amazon. To close my account, but keep the books and the #kindle as long as it works.
I'd be happy about pointers from people who have already done what I plan to.
Hints and and boosts are very much appreciated.