Environment: Ubuntu 18.04 Server running KVM. Guests managed via Virtual Machine Manager installed on a separate Lubuntu 20.04 machine. All guests running 18.04 up to now, all accessible via SSH and also via the console window in Virtual Machine Manager.
Problem: I upgraded a KVM guest running a working 18.04 minimal installation, to 20.04. The minimal installation is just about as bare as possible, just SSH selected in tasksel. Since the upgrade I get no console video output in Virtual Machine Manager for this guest. The VM appears to be working fine otherwise and I can SSH into it. Am using Spice channel for video and settings appear unchanged following the upgrade, but spice channel is now showing disconnected for this guest in virtual machine manager. Have also tried a clean install of a new 20.04 minimal guest on the same KVM host. Same problem, no video output. Spice channel disconnected.
18.04 minimal guests do not exhibit this problem. I am assuming therefore this is a missing/broken configuration in the 20.04 minimal guest. What can be done to restore video via the VMM console?