Search for "DeDRM", follow the first result you see to Apprentice Alf's blog. That should lead you to the GH repo with instructions.
It's still a bit of a pain, you may need to intentionally downgrade your version of the Amazon for Kindle app to an older version where the tools can break the encryption. But it can be done.
The pain kinda disappears if you have a physical Kindle. You enter the serial number once during setup of the plugin, then download the books from amazon.com/myk ("Download & transfer via USB" option), and just drag-and-drop downloaded files into Calibre's interface.
Works on Ubuntu too, which is really a PITA otherwise.
It's still a bit of a pain, you may need to intentionally downgrade your version of the Amazon for Kindle app to an older version where the tools can break the encryption. But it can be done.