If you want to convert M4B to any playable format, you need to convert M4B to MP3.
I have ever use UkeySoft Apple Music Converter to convert iTunes M4P songs, M4B/M4P Audiobooks to MP3.
You can read this guide about how to convert M4P, M4B to MP3
If you want to convert M4B to any playable format, you need to convert M4B to MP3.
I have ever use UkeySoft Apple Music Converter to convert iTunes M4P songs, M4B/M4P Audiobooks to MP3.
You can read this guide about how to convert M4P, M4B to MP3