[ps67]

Premise: of course when You buy from Amazon You receive trough Wi Fii the KFX if the book is enabled for "better typography" but if You download from the site You receive AZW3 or sometimes Mobi.

I use Ubuntu 20.04 and I downloaded calibre (actually 4.22) from the official site because this is the advice of Kovid Goyal, the creator of calibre. It works perfectly. I have never tried the distribution version so I have no experience with that.

I also have a Windows 10 dual boot that I use only for KFX plugin, ADE and Kobo Desktop. So my calibre in Linux handles my Kobo and my Pocketbook, my calibre in Windows 10 handles my Kindle.

When I bought my PC there was Windows 10 and I decided to not get rid of it, I said myself: "may be it could be useful for some strange reason", but I did not know yet that I would then buy my Ereaders and that I would need it especially for some programs that does not exist for Linux.

Of course You could use Wine: a person in the forum said that he was able to install Kindle Previewer with Wine, he is the only case I know, but the plugin doesn't work with Linux anyway.

You could try to use the Windows version of calibre with Wine and try to use the KFX plugin? It seems crazy and so difficult to convince calibre and the plugin to work. In my opinion after all it's not worth it but if you want to have fun...

ps: ADE is a strange beast: if You search You can see success in using it with Wine, while in this forum there are Linux user that reported a fail.

Edit: 4.99 is a beta version and, as far as I know, the DeDRM plugin doesn't work with it.