No, there is neither snapshotting of the root filesystem nor backup/restore of the hosts config files, nor a backup/restore of the whole host. If you screw something up, you would need to start from scratch and install PVE again. Keep in mind that Proxmox VE is a full Linux OS and not an appliance. It's like setting up a normal Debian/Ubuntu server with all the capabilities but also all the responsibilities this offers.
What might help is to backup the whole system disk (for example by booting into clonezilla) from time to time as well as regularly backups of all the config files (I would backup the whole "/etc" folder).