Calendar visible to all users on the subscribing domain (4290978)

QCS created calendars are visible to all users on the subscribing side

By default all QCS created calendars have default reviewer rights

This is by design and listed within the user guide:

If you select the Synchronize appointment details option, then the Reviewer permission will be set for the Calendar folder (for Default on the subscriber side), so any user from the subscribed organization will be able to view synchronized calendar details.

Attempting to manually set permissions over these objects will get overwritten by QCS and the only alternative would be to untick synchronize appointment detail - This change will impact all users in the publication and cannot be implemented on a single user basis.