Context: I am using the OG Steam Deck LCD version. 256GB.
As soon as I updated the SD using the stable 3.5 version, without changing any of the settings, I noticed that there were changes especially in the screen, it moves smoother and appears sharper. I booted up my game (playing Judgement currently) and somehow the FPS increased from 40s to near 60s! I checked all the other games, (NBA2k24, Hogwarts, and Nier Automata) and I am super sure the visuals have been subtly upgraded and the fps bumped up a bit. I’m amazed and it made my Steam Deck feel like new! :)
The stable update to 3.5.5 included some driver updates that probably increased performance. They also changed a lot of stuff with the screen and colour management. What you’ve noticed was valves hard work over the past month or so come together in the best update in months.