The workaround for a while was to have an old version of the Kindle for PC software on your computer and download the flies from there. You would get older versions that had crackable DRM.

They’ve pretty much closed this loophole. IIRC now you need an older physical Kindle that doesn’t support KFX files and you can download files for that device.

It’s still a crappy workaround because the older file format doesn’t have any of the latest typography features.