OK, so I think I understand what is going on. By disabling the repo_gpgcheck, the error message shown below threw me onto the scent that we have an architecture mismatch. I say "we" because ... I'm using docker to run a CENTOS/ROOCKY x86_64 system using an M1 Mac (emulating my steps from work, which is an X86_64 Mac). Docker downloads the ARM/aarch64 distribution of Rocky, but I'm trying to install the x86_64 packages. Something somewhere is detecting the REAL architecture of the system and installing a signing cert appropriate for it?? This results in a mismatch between architecture signing key and packages from a different architecture??
PostgreSQL 12 for RHEL / Rocky 9 - aarch64 1.6 MB/s | 1.7 kB 00:00 GPG key at file:///etc/pki/rpm-gpg/RPM-GPG-KEY-PGDG (0x442DF0F8) is already installed The GPG keys listed for the "PostgreSQL 12 for RHEL / Rocky 9 - aarch64" repository are already installed but they are not correct for this package. Check that the correct key URLs are configured for this repository.. Failing package is: postgresql12-server-12.16-1PGDG.rhel9.aarch64