I've finally managed to get my imaging PC working on Ubuntu 20.04 Focal Fossa, with an XFCE4 desktop and VNC server running. There were a few gotchas along the way, so I decided to document my steps to make it repeatable. It works to run the latest 64-bit LTS release of Ubuntu on an Intel NUC or a Raspberry Pi 4. I put it together as a gist on github. Hope someone finds it useful!