Fixed.
error: rpmdbNextIterator: skipping h# 2208
Header V3 RSA/SHA1 Signature, key ID 158b3811: BAD
Header SHA256 digest: OK
Header SHA1 digest: OK
error: rpmdbNextIterator: skipping h# 4578
Header V3 RSA/SHA1 Signature, key ID bdda8475: BAD
Header SHA256 digest: OK
Header SHA1 digest: OK
In my case, this message wasn’t telling me the rpm dB was corrupt. Instead, the message is saying the gpg keys on two installed packages are no longer valid.
After a bit of searching, I realized that key ID’s 158b3811 and bdda8475 are the signing keys for the rpmfusion-free and rpmfusion-nonfree el8 repos. Two packages with these keys must not have updated, despite having installed the el9 rpmfusion repo packages and then running a dnf update.
Knowing that, I ran the update again and simply removed all rpmfusion packages before updating to el9. I then reinstalled them after the update was successful.
Boom. Fixed.
Yes, you are absolutely right. Centos-backgrounds, centos-indexhtml, and centos-logos seem to be dependencies of several x11 el8 packages still hanging around. Removing those packages, however, results in losing my desktop. I need to look into this further.
This particular virtual machine is my sandbox for building (and breaking) things, so I might just leave it the way it is for now.