Katie is a rich text editor for Mobile and Desktop using Kirigami and KDE connect as a unique form of replacing servers
Something very useful that we could add are checkbox lists, so you can create todo lists and mark things as done by ticking the checkboxes.
Also I think that if we do a good job with the automatic sync, we don't need the screen with the "sync to device" buttons. I think it is a must to make auto-sync work 100% reliably, so if we have to add that screen is that we failed at that goal.
What if we just make it a Nextcloud Notes client instead of reinventing the sync ehm the wheel? :)
Or make the sync based on plugins, with one for Nextcloud and others for other online notes services.