This may be a silly question, but as far as online games that work, it shouldn’t matter if my friends are on Windows, right?
For the most part it’s fine like the other comment mentioned.
However there are a few edge cases like Borderlands 2 that is like pulling teeth to make work.
As an experiment I revoked the certificate that is used for code verification on the executable responsible for the popups. So far the only thing I broke was the .net installer. But no more pop-ups. :D