Scan shows updates, dnf says nothing to do

Absolute RedHat newbiwe here. running RHEL 8 here and trying to do a dnf update. A Nessus scan shows there are vulnerabilities on this system but dnf update says "nothing to do". I did a
dnf clean all and dnf check. The check showed nothing, just came back to the system prompt. I ran the dnf command after I did 'sudo su'. So it ran as root. dnf repolist shows all the repo's available. dnf list all shows the available files .
I would think it should be a simple problem.

Can I delete the files under /var/cache/dnf/* ?