Weirdness: My Authentik instance had a PostgreSQL upgrade prerequisite in order to update it.
I'd followed instructions 3-4 times completely unsuccessfully and had to keep reverting to backup.
So, I gave up for a couple weeks and left it be in order to get over my frustration.
Yesterday, I followed the instructions again. As far as I can tell, I did nothing different than I'd tried previously and it worked first try and then I was also able to upgrade Authentik.
NOTE: The instructions aren't exactly difficult! So, I don't see how I'd have gotten it wrong!