Give me a single reason why nintendo would even begin to consider partnering with valve.
Nintendo is famous for its closed and closely controlled ecosystem.
Partnering with apple to release a mobile game is a bad (outlier) example as nintendo has no capabilities to release their own phone.
Why would Nintendo invite/open competition with steam deck? Why would they make it easier to pirate their games and give steam cut on the sales via steam store. All the while nintendo has their own console their own store.
Its like apple allowed android store on iOS. Sure they could do it but why would they?