It seems like thre are really only a couple of options, and I haven’t found many review or examples that show enough detail to compare them.
Jellyfin has a bookshelf plugin that seems to be able to handle it. Audiobooks look to be accessed through the main client app, and ebooks through a companion app like JellyBook, which also claims to handle audiobooks.
On the other hand, there is Audiobookshelf, which specializes in audiobooks, but also claims to host ebooks. It has a number of client apps, but none that I found mention eBook reading.
I’ve found a couple of other solutions that seem more specialized. Maybe one of those?
I want to be able to read and listen on an Android device, preferably with a native app. I have a few comics, but mostly interested in books and audiobooks. I already have a Jellyfin server setup.
Sounds like Jellfyfin+Jellybook is your winner then. The server portion of audiobook or ebook hosting isn’t going to be giving you any game changing features. They serve files.
The client you use is going to make or break your experience here, so just go with the easiest setup on the server side, and then run through some clients to see what works best.