Ideally you only want to use game FSR if it has it. It’s usually FSR2, which is better than the FSR1 used by the quick access menu on the Deck

Combining multiple passes of it will almost always make it look worse than just lowering the in-game quality slider

If you have the game resolution set to below 720p and you enable both then you’ll be using the in-game FSR first, and then FSR-ing that up to 720p/800p.

Example:

You set the game to 960x540. You enable FSR in the game’s settings, and set it to Ultra Quality. You also enable FSR in the Deck settings. Here’s what happens:

First, the game is rendered at 739x415.
Then, it uses the in-game FSR to upscale it to 960x540.
Now, the Deck, receiving a 960x540 frame from the game, which is below native, runs that through its own FSR implementation, upscaling it to the native resolution of the Deck (or attached display), so 1280x720 for 16:9.

It will likely look terrible if you do this, but it’s entirely possible :D

It was never designed to be a ‘replacement’ for a regular gamepad. You can see this in all the marketing from back then. It shows people playing games like Cities Skylines on a TV, games that, to this day, still play terribly on controller.

It was designed to play PC only KB/M games. Not really gamepad games. The amount of FPS games I played with this thing, at a decently high level, is astounding. Plus the amount of mouse-only games too

Steam Deck made people realise how useful the trackpads are for controlling games, especially FPS or mouse-driven titles. Plus the Deck having a dock means you want a decent controller for it. Combine those two together and you get people wanting them to use when docked, since trackpads are super useful in some cases.

There’s a whole load of mouse-only games I’ve played docked to my TV using the Steam Controller, and it has kind of Just Worked.