This is not how umlauts and layouts work

That one works as well, but I dislike the way quotes work on that keyboard. I never got used to that.

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.

If you use the keyboard for desktop mode:

1. Open system settings
2. Navigate to "Input Devices", "Keyboard"
3. Go to the "Layout" tab
4. "Configure Layouts", then "Add"
5. Add "German (US)"
6. 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.

Bonus Umlaut of the day: Ö

German here. Nobody ever uses SMS, literally nobody. They are only used for 2fa.

Let’s be honest here. The amount of people this applies to is miniscule.