There will tend to be at least a little performance difference from Windows, but personally haven't tested it. I have an Index and it works great [0], though I really need a GPU upgrade (which is impossible these days, as others here noted). I only play on Linux so can't compare to Windows, but besides some little things not being supported like passthrough camera, base station power management (though you can do it through your phone), it works without any fuss.

[0] https://boilingsteam.com/the-valve-index-on-linux-on-a-min-s...