So I’m talking about playing previously Windows-only games on Linux, e.g. via proton.
I don’t know about the libraries etc that are used - is it possible for Microsoft to use some legal voodoo, for example, to suddenly end it all, and make the use of their libraries illegal (if they belong to Microsoft in the first place)?
Or could there be other ways of interference?
Not really. It’s basically the same as Google vs SCO. There it was Java libraries instead of Win32, but the principle is the same.
What Microsoft is already doing that hurts Linux gaming is selling software exclusively over the Windows store. It has some awful DRM that nobody has bothered to take on yet. That’s why the Windows version of Minecraft Bedrock Edition or the Gamepass app don’t run on Linux.
To give a bit more context: The outcome of that lawsuit was that APIs are not copyrightable in the US.
That’s relevant here, because WINE does implement the Windows API. It would infringe Microsoft’s copyright, if the API itself was copyrightable.
That Windows store never worked for me. I tried to buy something out of perceived convenience once, and tried to install some freeware once or twice (7zip and something else), and it never worked. On a genuine, activated Windows, that is. Never bothered to try again.