From a user perspective: Exchange Organization Sharing and calendar sharing

I want to share my calendar with a contact in another Office 365 tenant. I want to see his availability when scheduling meetings and I want to view his calendar in Outlook.

To enable availability we created a Organization Sharing on both end:

https://docs.microsoft.com/en-us/exchange/sharing/organization-relationships/create-an-organization-relationship

When I schedule a meeting I can see his availability in the schedule view and my contact is able to do that as well on his end.

Now, when I try to open his calendar (Add Shared Calendar, then typing his emailadres) in Outlook, I get a "You do not have permission to view this calendar". Inside an organization I would see the calendar but availability only.

Do I understand this correct that to open the shared calendar from my contact, he has to add me to the Sharing Permissions of his calendar? And likewise, for him to see my calendar, I add him to my Sharing Permission?

https://support.office.com/en-us/article/share-an-outlook-calendar-with-other-people-353ed2c1-3ec5-449d-8c73-6931a0adab88 

This seems to work on Outlook for Windows. I tried it on Outlook for Mac and the emailadres was not found and there was no button to explicitly add it.... Is it not supported on the Mac?