OK, I figured it out.
I must have somehow been blocked by the centos-webpanel server for some reason. I just blew away all three of my VMs, and reinstalled CentOS 8.4 (non-stream), and used a different domain name during the install process, and everything worked.
I'm not sure how this fixed the problem, other than maybe I was blocked, but maybe if it happens to someone else, they will know how to fix it.
Thank you everyone for the help, even though it didn't fix the problem, it gave me enough clues to figure it out.