One thing I noticed about cross platform sim games is that, frankly, they run horrible on native Linux. I measure like a 40% TPS drop, and even worse frame time spikes, in Rimworld and Stellaris.
The former is Unity, the later an in-house engine (Clausewitz). And they run fine in Proton.
Point being that you still have to be careful with popular engines, as the actual game dev still has to optimize it for Linux. If they can’t… honestly, targeting Proton is a fine alternative.
Windows is definitely, objectively dying.
The question is what fraction is replaced with Android/iOS and what with desktop Linux.