My Steam Deck arrived and I even got a setup for it. My problem rn is that my keyboard has an american layout but I need to type german umlaute sometimes...how do I do that?
Switch the layout on the "Taskbar" on the bottom right of the screen.
You can then use Umlaute like on any German keyboard, plus on the "a,U,o" keys themselves when you press AltGr (right alt). Any Sonderzeichen are like in the American layout. If you want to change that just use the normal German layout instead of German (US).
There is no way to change the layout of physical keyboards in the gaming mode. Those settings don't change anything in the gaming mode and but the gaming mode settings only work for the on screen keyboard.
Yes, as long as you have the [;' keys it will work just like it does with the German layout.
Even if you didn't have those keys, you could also use AltGr + a, AltGr + u andl AltGr + o for the Umlaut variants. I like to use those much more, because they seem much more logical to me Ü.
That isn't possible with the default German layout, which is a shame. I like the German (US) layout much more because of that.
There is no way to change the layout of physical keyboards in the gaming mode. Those settings don’t change anything in the gaming mode and but the gaming mode settings only work for the on screen keyboard.
You might be able to since gamescope (the compositor that the deck uses in game mode) supports keyboard layouts through XKB environment variables, but I'm not sure where to specify those on the deck (and it might even require write mode),