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.
After uploading a key, you need to wait at least 5 minutes. So try again.
If you have ongoing issues with keys, contact the vendor, e.g. via https://shop.proxmox.com/contact.php