Google API Service Account - Can't Access Private Data

Trying to access my personal calendar data using a service account.

I've gone through the setup for creating a service account (with owner permissions). Using NodeJS, I've successfully made requests to my public calendar, but not my private calendars. (same result using googleapis and google-oauth-jwt packages)

Everything that I've searched shows that I need to give "domain wide authority" , BUT, I do not have a G Suite account, so I don't believe this applies to me.

So the question is, can one access their own personal calendar data using a service account? What might I be missing?

via Red Twoon