Cromite is unfortunately chrome based, but
degoogled and hardened. I keep it updated straight from the github with obtainium. Ive been using both to bypass compatibility issues, but honestly I have more issues with cromite than Mull.
I’ve been using Librera FD. Not sure if it meets all of your needs, but it can be integrated with a Calibre server at least to grab your books from another machine. I haven’t bothered to see if it will sync what page you’re on though.
Mostly I use custom launchers because I don’t like the Google News feed and the general UI layout of the stock launcher. KISS launcher has been perfect for me.
Cromite is unfortunately chrome based, but degoogled and hardened. I keep it updated straight from the github with obtainium. Ive been using both to bypass compatibility issues, but honestly I have more issues with cromite than Mull.