I suspect I'm missing something basic, but:
Linux Mint 20.1 is now available. What I understand a standard upgrade is to open Update Manager, and under the Edit menu select a fourth, bottom entry to upgrade Mint.
However, when I pull up Update Manager, the Edit menu has Preferences, System Snapshots, and Software Sources.
I have run, for instance, an aptitude update and aptitude upgrade since linuxmint.com said 20.1 was available.