Brad White <b55white@gmail.com> writes:
>> Can you do a pg_dump of that database?
> Yes. No visible problems. No errors reported.
Well, that's quite interesting, because pg_dump ought to read
all the same catalogs that pg_upgrade is failing to read.
So I'm not quite sure what's going on there. Nonetheless,
your path forward is clear: use pg_dump (or better pg_dumpall)
and then load the output into a freshly initdb'd v12 installation.
It'll be a bit slower than the pg_upgrade way, but it'll work.
regards, tom lane