A Youtube video showing this was put up, but has now been removed.
You need a Graphic Audio account; and you buy the book using it; this is not a way to get it free.
The process is:
1) install an android emulator on your PC -- e.g. Nox Player
https://www.bignox.com/2) change its settings to root it.
3) run it, install Graphic Audio's app.
4) buy the book.
5) the app will download the audio file as an m4a into a subfolder.
6) copy the m4a from the simulator's storage to your PC.
I suspect the m4a is actually an m4b -- if it has chapters, then rename it to m4b.
Any comments, corrections, reply to
https://audiobookbay.lu/forum/audiobook-software-apps-and-resources/ripping-audiobooks-from-the-graphicaudio-access-app/ and this will be updated.