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.
Audiobookshelf for sure. It handles audiobooks fabulously, and it also does handle ebooks.
I use it to manage my eBook library, but not as the reader. You can set up a “send to ereader” option to email the ebooks to your reader of choice. So I just shoot them off to my pocketbook ereader when I want to read one.