I've been using radicale as my dav server for a year or two now. Coupled with davx5 it works really well on andoird and syncs well. Throw in a little wireguard

I've been using radicale as my dav server for a year or two now. Coupled with davx5 it works really well on andoird and syncs well. Throw in a little wireguard and you have a nice and completely secure (for private use anyway, locking it away would make shared calendars mildly annoying)