Restoring a full backup in Proxmox is quite easy. You can even do file-level restores!
- The VM or CT has to be stopped to restore it.
- Select the VM or CT and select “Backup”.
- In the upper right corner of the UI, make sure you have the proper storage selected that the backup was stored on.
- Select the backup you want to restore and click on “Restore”.
- Answer the semi-scary questions.
- Start the VM or CT.
I have tested backing up running VMs (snapshot) and then restoring them with no issues.