Calibre is great, but IMO it’s the wrong approach for this particular conversion. Use KindleUnpack instead, which is close to lossless.

https://github.com/kevinhendricks/KindleUnpack

This is a fantastic way to read books published by Tor on multiple devices. Now if only Tor would sell the ePub files on their website. (Tor eBooks are not DRMed.)

KindleUnpack doesn't seem to handle DRM though.

Neither does Calibre’s converter. To convert an encrypted AZW3 to an unencrypted EPUB, one can presumably decrypt it first and convert it second.

Calibre has a plugin the allows the converter to work with DRM

Removing drm from .azw3 is easy. [0] All you need is the ID of your kindle, since it's tied to your device.

There is also a plugin for Calibre, although I haven't tested this myself. I'm not sure if it requires a device ID or not. [1]

[0]: https://alexwlchan.net/2019/08/removing-the-drm-from-my-kind...

[1]: https://github.com/apprenticeharper/DeDRM_tools/wiki/Exactly...

I'm an author on Amazon and wonder: Is this also true if I switch off DRM for my books on Amazon? Could someone clarify this? I publish all my books without DRM.

So one thing I know is that for all the books by John Scalzi, their listings on Google Play Books have a note of:

    At the Publisher's request, this title is being sold without Digital Rights Management Software (DRM) applied.

(see https://play.google.com/store/books/details/John_Scalzi_Old_... for an example)

And indeed once you purchased his books you can download a DRM-free epub or pdf file of the book you purchased and use any tool you like to read it.

I don't see similar note on the listings of his books on Kindle store, so my _guess_ would be that Amazon is unwilling do fulfill this request from the author, but I could be wrong (I never owned any kindle device anyways).

The Kindle store doesn't make it obvious if something is DRM free anymore. The most obvious way is that DRM free books will usually list the number of simultaneous devices as unlimited while DRM books will not. Happy to be corrected if there is a nicer way of telling.