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?
Proton is built on top of wine for windows compatibility. The wine project has been very careful to independent build its compatible versions of libraries. There should be no Microsoft code in wine.