I think that for the backup server, it only need to check for the existence of proxmox-backup-proxy.service - I ran it and restarted that script. All works as it should now.

I'm not terribly familiar with the PR process. If someone could assist with this and wants to update the pve-nag-buster.sh I added the following code to my file and it cleared the nag on PBS. The install script will need something to identify PBS and change the repo from pve to pbs as well.

Add 2 Variables:
PBS_SERVICE="$(systemctl show proxmox-backup-proxy.service --no-page | grep 'ActiveState=' | cut -f2 -d=)" PBS="$(echo "${PBS}" | grep "NoSuchUnit" | cut -f1 -d=)"

And replaced the systemctl restart pveproxy.service with the following if block:
if [ "${PBS}" != "NoSuchUnit" ] then systemctl restart proxmox-backup-proxy.service else systemctl restart pveproxy.service fi

I was able to run the nag buster script with this on both PVE and PBS. If someone has a better way to identify PVE vs PBS/PMG, I'd be quite interested in how to achieve it.

Proxmox Backup Server actually has its own repository that is separate from PVE.

https://pbs.proxmox.com/docs/installation.html#proxmox-backup-no-subscription-repository

Same with PMG: https://forum.proxmox.com/threads/how-to-use-proxmox-mail-gateway-free-license.80130/

Just to make sure that it is getting the proper patches, that should probably be used instead.

I'm working on adapting this for my PBS server and can look into submitting a PR.