Just start the VM. If you want to access the VM console, you need a desktop environment on your Proxmox VE host.
E.g. https://pve.proxmox.com/wiki/Developer_Workstations_with_Proxmox_VE_and_X11
Please do not use such third party scripts (unless you know exactly what these scripts are doing).
If you want to upgrade from 7 to 8, please follow the official guide on:
https://pve.proxmox.com/wiki/Upgrade_from_7_to_8
irgendwelche third party patches eingespielt? wenn ja, bitte vor dem upgrade entfernen.
warum läuft so ein alter kernel und nicht der aktuelle PVE 5.15.107-2?
We do not have such a guide as this is most times not the best way to improve your detection results.
Did you follow https://pmg.proxmox.com/wiki/index.php/Getting_started_with_Proxmox_Mail_Gateway
I second this, please follow only the official - well tested - upgrade guides. Running third party scripts without deep analysis is a risk.
https://pbs.proxmox.com/wiki/index.php/Upgrade_from_2_to_3
Please remove firmware-linux-free, this cannot be installed on a Proxmox host.
Seems you did not installed this system with our ISO installer or installation guides.?
Seems this is a Symantec API for their NetBackup (all this is not "open" source), so not related to Proxmox Backup Server.
Please explain your use case, maybe this helps to understand your needs.