I have been using the Vulkan api (with high AA) for quite some time in VR with both my Rift cv1 and Vive Pro. I have preferred this over OpenGL because it gives me slightly better visuals (less shimmering). I have been using nvidia driver 446.14 but since I'm getting ready to upgrade my gtx1080ti to a nice new rtx3090 I thought I'd better update my driver to the latest series 3000 driver 461.33. I use DDU to uninstall beforehand.
Now Vulkan will not work on either headset. OpenGL works ok though. All my other Vulkan based apps like Aerofly fs2 and X plane 11.51r1 work fine with the latest driver. So, maybe RC8 needs a Vulkan update? Thanks.
Edit; Vulkan works fine in 2D mode on my monitor, just not in VR.