Well, depends on what your client OS is I guess. There’s a cli tool called proxmox-backup-client which allows you to back up OS level, I use this to back up the host OS of my PVE server. I am not sure if this tool is available for Windows/Mac though.

I have 2 PVE servers and on one I have installed PBS in parallel, which works fine. Just a different port to get to the UI: PVE: https://pve2:8006 PBS: https://pve2:8007