This tutorial is for arch linux, but you can adapt easily for others distros

https://github.com/KrumpetPirate/AAXtoMP3

• yay -Sy aaxtomp3

Install the dependencies:

• yay -Sy mp4v2-utils
• yay -Sy mediainfo

https://github.com/mkb79/audible-cli?tab=readme-ov-file

• yay -Sy python-pipx
• pipx install audible-cli
• pipx list then go to the directory apps are exposed on your $PATH at
• ./audible-quickstart (for interactive installation). (This will create files in a .audible folder)
• Retrieve the famous Audible authentication code: ./audible activation-bytes

Now that we have aaxtomp3 and our activation-bytes, go to the folder where the .aax file to be converted is located and run:

AAXtoMP3 -e:m4b -A activation-bytes -d audiobook.aax 
OR 
bash AAXtoMP3 -e:m4b -A activation-bytes -d audiobook.aax 

Note: Enter the activation-bytes code as is (without quotes).

Source(s) / Useful link(s) :

• https://github.com/KrumpetPirate/AAXtoMP3
• https://github.com/mkb79/audible-cli?tab=readme-ov-file