Make sure you set the # of processors to at least 2. I ran into the same issue as I always use 1 CPU with Hyper-V for everything else.
That was the problem. It was set to 1 one processor. I changed it to 2 and Windows 11 is installing. I hope it uses my Windows 8.1 home key to activate. I thought about using my Windows 10 Pro key but I don\’t want to use a key already being used.