Generally the in game settings are up to the developer to implement. Many games generally have a detector of some kind that automatically configures the game to usually either high or low settings. But overall, game optimization from devs is not something that can be relied up on.
But Valve does do a few things which make them unique over a traditional windows pc experience. Because Steam deck and machine are fixed hardware, Valve does pre-compile the shaders which significantly reduces to eliminates shader compilation stutter from various game engines for developers who do not do it themselves. That along with sleep/resume and slightly faster performance on Linux does help the game experience quite a bit.
PC Specs: CPU: 7800X3D || GPU: Strix 4090 || RAM: 32GB DDR5 6000 || Main SSD: WD 2TB SN850
