Recently Red Dead Redemption 2 had a big update which amongst other things, added in FidelityX Super Resolution (FSR) 2.0. Sadly, it broke it on Linux and Steam Deck but Valve already have a fix out but you need to pick it manually for now.
Valve updated Proton Experimental with the fix needed to get it working again, showing how they're clearly paying attention to some of the bigger games.
Additionally the September 7th update of Proton Experimental also got these games working:
- Deathsmiles II
- Primal Carnage: Extinction
Note: for Proton Experimental on Desktop Linux, you now need at least Mesa 22 / Nvidia drivers 510.47 or newer. Changelog available here.
Here's a quick run over the changes and a quick-look at Red Dead Redemption 2 running again on Steam Deck: