Steam Deck docked Resolution

I installed Lutris on my Steam deck via the Discover Store.
I have also installed some games in Lutris, all run without problems.

When I start them in Gaming Mode I have the correct resolution in the game settings (1280×800).

When I have my Steam Deck in the dock, it only shows the same resolution, no 1080p possible. In the Steam Deck settings I have also changed from “automatic” to 1080p, so that a full HD image is sent. However, in the game settings only 1280×800 is possible.

When I have my Steam Deck in the dock and start Lutris in Desktop Mode, I also see other resolutions in the game.

But I want to play the game in Gaming Mode (because of the overlay and the correct visualization of the buttons in the game).

I read that you can force lutris to have the resolution you want, but in the lutris settings the Gamescope function is grayed out.

Does anyone have any ideas?