@schwim
As far I read on internet and benchnatks, If you have a working #Vulkan, the average performance between Windows and #Wine (proton) is equal. That means also, there cases where a Windows Games performs beter on a Linux with proton.
I assume the cause is also that some gamedeveloper enhance a game for steam deck also.
I propose to retest your case again.
Microsoft is blocking Windows Customization Tools (www.neowin.net)
TLDR: StartAllBack, ExplorerPatcher and some other projects are being blocked on 24H2....