This should not be needed and can in fact cause problems. While we are still working on the documentation, we are effectively not supporting EPEL being enabled on a Katello install for EL8.
I would also suggest enabling the postgresql:12 module before installation. We are working on a before GA fix that will help ensure that by default postgresql:12 is enabled via the installer. EL8 has PG 10 as the default and starting with that would cause undue upgrade pain later.