I use Librera on Android. I generally convert to .txt when I read fiction on Linux because I can use a wide range of text editors/viewers that way. It has been a great way to familiarize myself with a lot of features that I don’t use when I’m tweaking config files.
Beyond that, I use Okular or Calibre’s reader for epubs on an as-needed basis.
If notetaking is going to be your primary use, you’ll definitely want to focus on the keyboard experience. Touch-typing on a screen isn’t a fun way to take class notes and a lot of cheap bluetooth keyboards end up being laggy or otherwise unsatisfactory.
I’ve heard good things about Surface tablets and their attachable keyboards. I’ve personally had good luck with two-in-one laptops, where the keyboards are built-in.
When/if you try for a pure tablet experience, be prepared for rough edges. Outside of KDE, Gnome and maybe Budgie, most desktop environments/WMs aren’t designed to work on tablets without keyboards. Getting an on-screen keyboard to act how you want it to act isn’t something that has been solved universally. Another fun wrinkle is that there’s no guarantee that the tablet’s accelerometer will be detected, so it may be challenging to rotate the screen orientation. If you like messing around with settings and downloading half-finished projects from github, then you’ll love playing around with Linux tablets.
I’ve had the large file issue with Librera too. Bundled epub collections with absurdly large page counts have sometimes been extremely slow to load. I’ve had better luck recently, so it might be a partially solved problem.