The Proton Experimental branch received a bunch of fixes and tweaks for the Steam Deck, mostly for game compatibility but also adding HDR options for Mass Effect Legendary Edition and Injustice 2.
The latest changes are:
Fixed multiplayer in DiRT Rally.
Made HDR options available in Mass Effect Legendary Edition and Injustice 2 on capable hardware including Steam Deck OLED.
Fixed experimental regression causing Melty Blood: Type Lumina multiplayer to crash.
Fixed VRAM reporting and outdated graphics driver message in The Last Of Us Part I.
Fixed VR compatibility with L.A. Noire: The VR Case Files and GTA V R.E.A.L. mod.
Fixed experimental regression causing Injustice 2 to render as incorrect size.
Fixed more memory leaks with Final Fantasy XIV launcher.
Fixed a few Proton 8.0 regressions:
The Binding of Isaac cursor no longer desyncs when toggling fullscreen.
Improved load times in FINAL FANTASY XIII-2.
You can see a full list of changes currently in the Proton Experimental branch here.