My problem is similar, but different! Runs great in 2D, Ctrl-Tab into VR and it runs great. Ctrl-Tab again to exit VR and… wait for it… eventually something happens. It is running slower, MUCH slower, than a slideshow. So slow in fact, that it is just about impossible to select anything. Only escape is Task Manager and Exit the Sim!
i5 9600K OC’d 4.85Ghz, 32 GB Sys RAM (DDR4 @ 3200), RTX 3080 Ti (12 GB VRAM - MSI Suprim), 2 X 1TB NVME SSD.