I found this comment https://www.reddit.com/r/metroexodus/comments/fdxyz9/comment/fp8qgdb/
it's definitely related to r_gamma, but only on regular edition with DX11
Default is 1.
Setting it to 0.5 makes the problem extreme, setting it to 1.5 just about solves it. I think 0.5~1.5 is the range, since setting higher does nothing.
Can it be fixed on DX12 or Enhanced? I want to play Enhanced Edition for the RTX and DualSense features