Why can I see shared Exchange Calendars on my iPhone but not on my Mac?

A client shared a few Exchange calendars with me, and I clicked on the emails to accept the calendars. I can see them as expected on my iPhone but they're not populating my Mac.

I can see my personal calendar on my Mac (using default Mac Calendar app and Fantastical on my Mac) but the shared ones are only visible on Mac Outlook - but I want to use the default Apple Calendar app - so it needs to work there. Other app tests are merely for background info.