Calendar - google imported event - read only?

Hi - this is an issue that has only appeared since the Sequoia update *I think*.

A shared google calendar event can be viewed and editted in Apple Calendar. Fine so far.

BUT if the google event has another invitee added to the event, then the event becomes 'read only' and I can no longer edit or add notes. The wording on the event is "This event was imported (read-only". If I remove the invitee I can freely edit the event again.

The shared google calendar is a Google Workspace account...

Any ideas??