Broken upstream modular RPMs reported as upgradable to
An upstream user reported that, when Rocky released modular nginx RPMs without tying them to module streams first, they appeared as upgradable for the host. The important thing here is that dnf new that these RPMs were not installable, but Katello thought they were. It's possible that the bad RPMs were marked as modular by Pulp.
To reproduce this, try using the Katello test repositories to make modular RPMs that belong to no module stream. If they show up as applicable, we've reproduced the issue. If that's not the problem, then more investigation will be needed.