I used to use Audible, because it was convenient and cheap for single audiobooks. Now, I migrated away from it by using Libation – a great project to download Audible content – Jellyfin for managing the audiobooks, and BookPlayer on iOS, the latter came through a suggestion from @simon@dewp.space.
Absolutely recommended. Especially the app is so much faster than Audible, which takes ages to even display anything. And way less battery-consuming.