Invitations in Calendar: cannot invite users

On Nextcloud 23.0.5 and 21 and 22, I would like to invite people to attend an event created in my own NC calendar.

When I click on “Attendees” I cannot find any user of my system.
I can set an email as ‘attendee’, however this is not what I want…

I want NC users on my system to get an entry in their own calendar, letting them know that I sent them an invite for an event I am planning.

Any idea ?

Thank you