On a RTX3080 and Ryzen 3800x, you can be either at 90fps in low quality, or 60fps in high quality at all time. I suggest that you update your NVidia driver and SteamVR, and ensure that no application is using the GPU memory.
Thanks for the reply. Everything is updated so that's not the issue. Whenever I play ComeCloser I always experience this low FPS problem (massive latency spikes, reprojections, low GPU utilization). If I switch to any other VR game (HL: Alyx, Contractors, H3VR, Boneworks) I can consistently achieve steady 90 fps.
Does it make any difference if the game has not been added to the Steam library and is launched directly from its directory instead?