Hi Sampson… you may already have figured this out by now, but I ran into the same situation so I thought I’d post a solution in case anyone else finds this post through a search engine like I did today.
I had a Fedora 32 (KDE spin) guest running in virt-manager on a similar F32 KDE host.
After a long idle time, it went to sleep. I came back to a black screen in virt-manager showing only the text “Guest disabled display.” and nothing I did with the mouse or trackpad or keyboard would wake it up.
I was still able to SSH in from the host so the guest was awake, but I wasn’t sure which process(es) to kill or services to restart to get a login screen to come up again in the guest. And of course, I didn’t really want to kill any processes!
I eventually figured out that if I used virt-manager’s Send Key menu to send CTRL-ALT-F2 to have the guest switch to a terminal session, I could then immediately use the Send Key menu to send CTRL-ALT-F1 to switch the guest back to the GUI desktop login screen (in my case, KDE / Plasma I guess).
Hope that helps you and/or someone else out!