Valve backed Linux because Newell saw Microsoft Store as "unfair" competition(He felt MS could easily monopolise the platform lol) back in 2013, think they put the whole thing on life support when they realised it's not, the number of Steam users on Linux hasn't really budged since 2013 regardless of the software library.
MS's moves to make it a viable platform again might have instigated the proton layer development but it doesn't look like it's changing much regarding the wider issues of gaming on Linux & its market penetration(0.8% on Steam hardware survey).