This is my experience too. However, there is nothing special a game needs to do to support VRR. So the fact that VRR works fine in this game under Windows but not Linux makes me think there is a bug in Proton, the compositor, or the GPU driver.
I can say with 100% certainty that VRR is working as expected under Windows 11 with my RTX 3080. I haven’t tested in Fedora yet.