This issue does not occur for Office 365 accounts that are using the REST protocol for Calendar.
This issue is caused by a limitation in the EWS protocol that is used for Exchange on-premises accounts. Office 365 accounts that use REST are no longer affected by this issue.
In Outlook for Mac, you must have at least the Reviewer permission to access the other user's default Calendar folder so that you can also access any subcalendar folders.
For example, you have permissions to the following shared Calendar folders:
- Second Calendar
In this example, Second Calendar is a subfolder of Calendar. This is displayed as follows.
To be able to open the other user's Second Calendar folder, you must have at least the Reviewer permission to their default Calendar folder.
For more information about REST for Outlook for Mac, see Outlook for Mac improves calendar sharing performance with REST.
For more information about how to share a folder in Outlook for Mac, see Share a folder in an Exchange account.