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?
Even then you can still have someone read the source and write a spec for a second programmer to write a library. The programmer never saw the source code but it was still useful. Still legal to do this. If someone dumped original source into the projector could be similarly checked for duplication without breaking the law.
That’s true, but white room reverse engineering requires two people to do what one person could do by just stealing the code. Plus, the person reading the source code would be “burned”, they can’t work on normal implementation after browsing the source.