There's a new way to liberate purchased Kindle books from Amazon's DRM.
https://blog.pixelmelt.dev/kindle-web-drm/
A few points to note:
* Hardcoded to the .com store, but trivial to change to .co.uk
* Uses OCR - so some odd / annoying mistakes - especially around punctuation.
* Every line is wrapped in a <p> element - which breaks reflow.
But, other than that, remarkably capable. Once you've got your session token, it only takes a couple of minutes to get an ePub.