Arch everywhere (desktop with KDE, personal laptop with GNOME, work laptop with COSMIC, a remote raspberry pi) except a Raspberry Pi Zero (Raspbian) and the Steam Deck

Why not work with standard CarDAV servers?

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.

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)

Dino is good.