Thx, seems that webdav was used by some apps for users that don’t want to install their own / non-cloud caldav server (e.g. icssync that is no longer maintained).
Found a chinese, closed source alternative (not reliably working, but am desperate):
Or setting up Baikal on Fritzbox, but then all mods will be gone after an update and I guess one is exposed to the internet:
Or google or the closed source, paid / beta https://generalsync.com/de/
All far from perfect, still think the use case of users wanting to sync with their local (ics) files is valid, to avoid the cloud.
However, thanks for the cool & solid DAVx⁵ & ICSx⁵ so far