No calendar invitations sent

I got a really weird problem with my new blanc instllation of nc on alma linux:
We use actually 2 accounts, mine which is admin, and another account which has no special privileges.
I can create calendar items and invite the other use. This user receives the invitation. Fine.

Whereas the other user can create calendar items but when he invites me, I don’t get any message or see the apppointment.
I tried using the nc web and a mobile which is connected via DAVx. In both ways, the calendar item is created and as an attendee I can see myself, but my account doesn’t receive neither email nor anything in nexctloud.

The nc log has no special entry.

I’ve just updated to the latest version 25.0.4 but the problem still exists.

Any idea why this is?