Valve has been supporting Linux before Windows 10 was even announced.
They started in 2013 with a Debian based distro for the old Steam machines.
Gaben stated back then that Windows 8 and Microsoft's attempt to monopolize gaming to the Microsoft store was 'catastrophic', and he was right. Because of that decision I've been using Linux since 2016, and I stopped dualbooting once and for all last year :)
I'm also aware of the deal with Arch, makes me really happy.