Valve should. Valve is the one making these games available for purchase on non-Windows platforms. Ubisoft never supported this.
it sounds like you're suggesting valve should be restricting which games they sell depending on the platform you are viewing from?
that would be annoying, and ultimately futile. i purchase games from my phone to play on my pc, or from one pc to play on another. i purchase windows-only games and mess around to see if they can work with proton. etc. i do not need valve to coddle me like that.
"system requirements" is at the bottom of every listing.
That's a totally reasonable ask.
the developer says it is windows only. a 3rd party, not the developer, says the game can work on non-windows. who should you believe? a real mystery.
maybe the kids arent alright
So you expect them to deny refunds and then say "hey you shouldn't have believed us"?