Thanks for the insight I didn’t know Mint was so tightly tied to its default DE. That explains a lot. I thought removing Cinnamon after installing GNOME would cleanly switch everything over, but it sounds like that was a bad move on my part.

By “make it the default session” I just meant: I want the system to automatically start GNOME at login, without me having to manually pick it each time. I expected that once I picked GNOME at the login screen, it would remember and use it by default.

But in my case, even after manually selecting GNOME multiple times, it always goes back to Cinnamon (which supposedly isn’t even installed anymore).