I'd mentioned removing Audible / Amazon DRM without having to resort to some sketchy web site.
There's an 'audible' commandline that can manage, dl and decrypt audible library items. It can even handle multiple regional libraries. You'll need to auth once with Amazon's servers, but from then on, your key is stored.
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Based on: https://audiobookbay.lu/forum/guides/audible-aaxaaxc-convert-mp3opusm4b-linux/
Software:
* Audible -- https://github.com/mkb79/Audible
- Audible CLI -- https://github.com/mkb79/audible-cli