This isn’t really a direct answer to your question, but a bit of info just in case it’s helpful. I found references to some tools from a company called Epubor but not to sure about them and want some info from other users first. Updated the de-drm plugins in Calibre to the latest versions but they still won’t remove the DRM. I tried the suggested new replacements: Download from the web to an old kindle device using the feature to transfer by USB to get an older. Old revs of kindle app don’t work on Catalina and the new file formats are all DRMed even from publishers who have said no to that outdated technology. Not to steal or hurt any authors but because I want a free and usable copy of the books I buy. Procedure was to download books in old kindle app, I had a Hazel job watching the kindle folder and copying the various book format files into a convert folder and a Calibre process to automatically run the items in the convert folder through de-DRM and bring them into my Calibre library.

My old method was to use Apprentice Alf’s DRM removal tools running under the older rev of Kindle app.

Dedrm calibre plugin modefied