Invite circles to appointments

I have already asked my question in the German sub-forum, but I did not receive an answer there. I hope it is okay to ask my question here again.

I am using a managed Nextcloud 26.0.4 Enterprise by IONOS.

When I create an appointment and want to add participants to the appointment, I can only add individuals, but not entire circles. (Sharing a complete calendar with the created circle or files works.)

Is there a reason why circles cannot be invited to an appointment? Or am I doing something wrong? Thank you very much!