Radicale is maintenance-free in my years of experience.

Doesn’t Etar use DAVx⁵? I would love direct synchronization but I don’t see a way to connect directly.

Open document text is a subset of open document format

Thanks :-) I don’t have an Apple device so that would be very challenging but a web UI version is in my todo list (I think it’s possible with the GUI/Iced interface)