Calibre allows you to maintain a library of you ebooks and sync it with devices (including Kindle). It is also able to convert the ebooks to all formats you need.
I mostly use it to get ebooks from z-lib and put them on my Kindle. But it works the other way around, too.
Last time I did probably close enough to this (kindle ebook to drm free format that works on anything), I had to use a patched old version of the kindle desktop program together with calibre and some drm removal plugin. The ebook had to be downloaded for the first time with the patched client or you would be stuck with the newer drm that at the time and probably still now hasn't been figured out.
Just use that I stead of the apprenticeharper version the guide links you to. I haven't used apple pc's since the PowerPC processor days so I'm not sure where to safely get old version mirrors of kindle desktop.
Kindle isn't based on Android; it's bare Linux with heavy DRM and a very limited ebook reader app on it. Whether the MacOS kindle app would help, I don't know.