friend should nuke this crapware and use syncthing for such activities. if they happen to run jellyfin, they can use it to serve books as well, and by utilising the OPDS plugin it would allow compatible readers (e.g. Librera) to directly download books/comics to the device in a shop-like interface.
I wanted to write the same thing. have the notes app do the notes thing and handle encryption elsewhere.
as to apps, I suggest QOwnNotes. it’s markdown, highly configurable so you can make it minimalistic AF, stores notes in invidual files and folders. it also has a bunch functionality like syncing to nexctcolud and such, but I’d advise against it, just use it as a notes editor. you don’t have to selfhost anything, make it use the e.g. Documents/Notes folder and you can use syncthing to securely replicate it to other devices.