I was really dissatisfied that notes are always somehow weirdly shared with a propriatary backend. There is jtx Board which uses your CalDAV calendar (Nextcloud, Radicale, etc.) as a backend which is really cool. The UI is also OK, but there seems to be no (Linux) desktop app for that.
So I started https://github.com/jeena/JNotes because I was curious about developing for GNOME anyway. It's going very slowly - because I am a stay at home dad with a one year old who demands all my attention :D - but it's going forward, but I guess it'll take another year before it's usable ^^.
Actually I was hoping that there would be more notes apps using standard backends like CalDAV or IMAP, but it's almost impossible to find something, everyone seems to want to implement their own backend and then charge for the synchronization.