@maximilian said:

The ROLE is still different from yours, but that shouldn’t make a difference, right?

Right, as long it’s a role where RSVP makes sense.

You could have a look into the source code of AOSP calendar to find more information.
I cloned the repository and grepd for it (grep -Ri role .) but I got no hits…

In Android terms, it’s called ATTENDEE_TYPE (see SDK docs).

I don’t know, but I guess that OwnCloud doesn’t support CalDAV Scheduling.

If I understand it correctly, then owncloud uses sabre for the calendar - and they say on their website they support scheduling. I have verified that my owncloud installation has the required settings…

As far as I know, OwnCloud is based on SabreDAV, but it has a special way for many things. Maybe CalDAV Scheduling is just not enabled in OwnCloud for some reasons?

From my point of view the issue is now resolved at the DAVdroid end: I know that I can’t use the Google Calendar App (=> use Etar) and I need to fix my owncloud / switch to something else (do you have recommendations?).

I still didn’t find anything that’s matching all my needs https://davdroid.bitfire.at/configuration may be a good starting point. If it’s about feature completeness, I think Contacts & Calendar Server may be interesting, but I don’t have experience with it.