Yes, I restarted Proxmox early in the troubleshooting. Later I even updated the host from Proxmox 6.4 to 7.2 so it has been restarted multiple times. The guest has also been restarted several times.
The result is the same after the restarts no matter if I connect at the console in the browser, with novnc in a window, with the built-in Windows RDC tool, or my preferred connection manager mRemoteNG.
I get the Windows login screen and after logging in as any user the desktop is black. I can press ctrl-alt-del and get the selection screen with Lock, Sign Out, Change a Password, and Task Manager. The first 3 choices do what is expected. Task Manager opens the window for about 1 second then goes back to the black screen. I can't get to the Run dialog to start Device Manager or anything else.
This VM is a Windows home server for me and all of its background functions are working fine, I just can't log into it. Very frustrating. I should have some more time to look at it tomorrow.