Note that it turns out that until Katello 4.8.1 is released, the repos used by Katello 4.8, are missing the new rubygem-pulp_deb_client-2.20.2-1.el8.noarch.rpm to go with the patched pulp_deb version python39-pulp-deb-2.20.2-1.el8.noarch.rpm (which is available for Katello 4.8).
Apparently this causes problems during regular pulp_deb usage. See this post for a workaround.
Sorry for the bumpy rollout.