It’s not really about OS differences - as the GP said, games don’t typically use a lot of OS features.

What they do tend to really put a strain on is GPU drivers. Many games and engines have workarounds and optimizations for specific vendors, and even driver versions.

If the GPU driver on Linux differs in behavior from the Windows version (and it is very, very difficult to port a driver in a way that doesn’t), those workarounds can become sources of bugs.