It is still possible if you have an old enough Kindle. I have a 1st gen paperwhite and can just connect it via USB to my PC and pull books off the kindle with Calibre and then remove the DRM.
Though if you’re wanting to remove DRM from Kindle Unlimited books, you’ll have to actually edit the DeDRM plugin code, as by default its set to not let it be run on KU books.
NexusMods is working on their new post-vortex mod client, which does have Linux support. It can be found here on github.