Currently using the puppetlabs-puppetdb module on el8 requires a bit of repo management to get working (see https://github.com/puppetlabs/puppetlabs-puppetdb/commit/2c0d17e4a148377613952d45a8ecad83e8837697).
I think the dnf management feature added here could be the solution https://github.com/puppetlabs/puppetlabs-postgresql/pull/1239/commits/8d0efec9fb5a5df42ed64375c71a11d8b6f90b4c