It specifies it's from the app, so they have access through the native functionality for that. When you go to install it, it lists the data it accesses, and by downloading and using it, that's how they are given permission.
Protip: Don't use the app
I have different expectations for different games. Generally I want the battery life around the 3 hour mark, though; if it can't hit that, I don't really want to play it on Deck.
I prioritize framerate over graphics 100% of the time. If a game hits 60FPS but I have to drop all the graphics settings to Low, that's a W for me. For AAA stuff, I'll do 30FPS if I don't have to drop the resolution too much, and if that 30 is STABLE.