It still works for Amazon but it doesn't really work for books in their newer KFX format. It's best to use an older version of Kindle for PC or use their download and transfer to USB if you have a physical eInk Kindle to get an AZW3 file which should unlock no problem.
Installers for older versions are becoming increasingly elusive, I've found. Anything newer than Kindle for PC v1.26 and DeDRM can't break the encryption. Installers for v1.17 or v1.19 can still be found, but on Linux those versions can't connect to Amazon because one of the SSL certs used by the app has expired.
That leaves v1.21 as the "sweet spot", but most of the sites that used to host that installer EXE have mysteriously disappeared.
That workaround gets you the text but it's missing a lot of the recent typographic improvements. It's fine for extracting text for TTS, but isn't ideal if what you are trying to do is maintain a DRM free archive of books you've purchased.
It's like saying you can break BluRay DRM by recording the screen with your phone camera.
Stuff like drop caps, kerning that isn't terrible, hyphenation, and better word spacing. None of it matters if you are feeding the text to a speech synthesizer, but it can make a difference when reading.
Some of that stuff you can get back by using an ePub version and reader from the AZW3 file which can typically be done using KindleUnpack. Some of it is less the file format and more the rendering engine used and they simply haven't bothered to backport it to their AZW3 renderers. Amazon does AFAIK precompute some stuff like hyphenation but not everything.
Also does a very good job of metadata management and format conversion. I don't know of a better solution. With Calibre you can buy wherever you like and maintain the format and metadata system you prefer.