Backup a Raspberry Pi to Proxmox Backup Server using the Proxmox Backup Client

This works on a Pi 4, and should work on a Pi 3, but to work on a Pi Zero you would have to figure out how to compile your own client. More info in this thread on the Proxmox forums.

Determine if your Pi is 32bit or 64bit

Run the following command. If you get arm64, it's 64bit, otherwise you'll see armv7l which is 32bit.

uname -m