Notesnook and Standard Notes are really good. Both are end-to-end encrypted and FOSS.
Every other app and solution I've tried is kinda janky, e.g. using Dropbox, git, Syntching or some other app to sync across devices. I want an all-in-one, encrypted, cloud-based, FOSS solution.
I've been using Standard Notes for some years now and I'm pretty happy with it.