Through a long series of events that I won't recount here but have documented here https://www.reddit.com/r/oculus/comments/ah5ubq/ok_question_about_virtual_desktop_in_new_home/
I think I have determined that the mouse actions on the desktop in home require some permission that isn't available to standard Windows accounts. Other virtual desktops work so there's no good technical reason for this.
Running in an Administrator account, particularly for gaming, is not good form although it's fairly standard in the Windows world. Hopefully Oculus will fix this but mostly I'm posting up in case anyone else is running into the same issue and is pulling their hair out.
If anyone knows which permission in particular is required, I could apply it individually to that account but I'm not going to give it full-on admin access and will just do without the virtual desktop for now. It would be really nice to be able to use it.