I've tried removing all previous versions of Excel and reinstalling. But no luck. I got the family version with using dynamic arrays in mind. 

I assume you mean you got a family subscription to Microsoft 365. That's what I have as well, on the Mac. What you don't mention is "signing in." You should have a user id (typically your email) and a password, for Microsoft. I know I use the same combination of ID and PW for OneDrive as well as the Office suite. And it's all a personal/family account, not