I suggest you check out Decky FrameGen.

The technicals are … very complex, but the upshot is: It basically injects FrameScaling/FrameGen modes into games that don’t officially support them on AMD hardware.

So… I’ve done this with CP2077, and if I understand this right, basically it injects FSR3, but under the DLSS settings under the game’s options menu… and it works better than the game’s current officially supported FSR 2 for the Deck.

Elden Ring may also be able to benefit from it.