How are they forcing developers? If developers don't think it's worth it to make their game compatible with Steam Deck, can't they just avoid doing that?
Besides, if this does end up putting pressure on the developers to start supporting more platforms than just Microsoft’s data collector ahem I mean, Windows, then I’m all up for it. It’s a win for everyone.
Otherwise, I can't remember the last time they funded a game they didn't make themselves. Maybe in the very early Steam days, but that's long past.