How to find and download Kindle books on Mac OS Sonoma 14.6.1?

I'm desperately trying to find the ebooks I read via the Kindle app on my Mac.

It's regular Kindle, not the Unlimited version.

I want to get the actual file to keep safe offline if Amazon starts to make them disappear, and I want to be able to convert them to other shareable formats.

[Re-Titled by Moderator]