Microsoft locking out third-party applications with Windows S, and/or pushing users to Microsoft's own game store, was actually a real threat to Valve. That's one of the major reasons Proton is a thing: Valve realized they were entirely dependant on a party they had no leverage over, so they built and invested in Linux.
Should Microsoft ever make a move now, Valve isn't completely at their mercy.
Valve is still at the Microsoft's mercy to tolerate Proton's existence.
They should have made it attractive for developers already targeting UNIX like systems, with PlayStation and Android NDK, to actually bother shipping GNU/Linux builds of their games.
> Valve is still at the Microsoft's mercy to tolerate Proton's existence.
No, they aren't. Valve is way, way too big a bear for Microsoft to poke. If they banned Steam, the backlash would be severe.
It would also result in even more users switching to Linux to keep access to the games they've already paid for, and which work under Linux due to proton.
Microsoft is at Valve's mercy. Valve doesn't need Microsoft, but Microsoft very badly needs Steam around to keep gamers on windows.
The outrage would be massive, that would be giant scandal