Self-hosted install fails with "su: user postgres does not exist"

If a self-hosted install on RHEL fails with the following sequence of errors:

Importing GPG key 0x442DF0F8:
Userid : "PostgreSQL RPM Building Project "
Fingerprint: 68C9 E2B9 1A37 D136 FE74 D176 1F16 D2E1 442D F0F8
From : /etc/pki/rpm-gpg/RPM-GPG-KEY-PGDG
Unable to resolve argument postgresql
Error: Problems in request:
missing groups or modules: postgresql
Failed to enable unit: Unit file postgresql-13.service does not exist.
Failed to start postgresql-13.service: Unit postgresql-13.service not found.
su: user postgres does not exist
su: user postgres does not exist
FATAL Installation failed: exit status 1
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The most likely cause is that the RHEL system has not been registered with RedHat for software updates.