ah thanks for the clarification @obacht, sorry @jollajo. But it would be just icsx5 that’s needed for the sole reason to subscribe to .ics / icalendar endpoints, not the whole of davx.
You can do intra murena.io calendar sharing if you name the explicit email address btw - Share calendar with other /e/OS users - #2 by tcecyk
it’s pretty involved to share across the silos in any case