

Depends on what you’re doing a bit. Databases? Hypervisors? Just files? If all of the above, its best to use an actual product this. Either foss like borgbackup or Urbackup, or something like Veeam which is a popular pay option.
If its a proxmox hypervisor, they have their own free backup appliance, but you need a second physical server to run it on.
If it’s just databases, most have a built in way to take a backup. Just google the name and backup. Make sure it’s running automatically and is moved to a separate server on each run.
For files, rsync is a great option.
OP, If you dont have a proxmox vm template ready to go, here is a great starting place using cloudinit:
https://github.com/UntouchedWagons/Ubuntu-CloudInit-Docs
You can use this with the proxmox gui cloudinit config as well to add your ssh key to each vm/etc.