Proxmox - Guests (VMs and Containers) - Install a GUI - A full desktop with all the extras

Choose one of these: 

sudo apt install lubuntu-desktop

OR 

sudo apt install xubuntu-desktop

OR 

sudo apt install ubuntu-mate-desktop

OR 

sudo apt install ubuntu-gnome-desktop

OR 

sudo apt install ubuntu-desktop

OR 

sudo apt install kubuntu-desktop

NOTE: This will install everything that the live cd of each Ubuntu flavours.

  • This means even the media players or whatever they find useful for their flavor.

References

https://lubuntu.net/

https://mate-desktop.org/

https://xubuntu.org/