If you want to backup your VMs and Container, the best easiest method is the proxmox backup server (PBS), highly recommended. There is no real need to backup the proxmox host system, it can be newly installed from the iso, but since it is a normal Linux system it CAN be backuped with every backup solution which can backup linux systems. It is a debian system based on an ubuntu kernel to be precise.
The important data is the config in /etc, including the proxmox configs in /etc/pve.
So disaster recovery:
1. setup new proxmox
2. configure networking and storage the same as before
3. attach your PBS storage
4. restore your virtual machines