Unable to change output resolution to external display in Game Mode

[Rezzyk]

I spent some time today trying to get my Steam Deck set up to my TV and ran into an issue that makes games basically unplayable in Game Mode.

It seems like Game Mode outputs at 4K to my 4K TV with no way to change the resolution. This makes games really choppy, and changing the resolution in the game itself, or adjusting scaling/frame rate caps, does basically nothing.

However, then I went into desktop mode, set my TV display to 1920x-1080/60hz, set it as primary and disabled the Steam Deck display (I had to do this or games kept launching on the Deck).

After that I opened Steam in Desktop Mode and ran a game - Ori, to be exact. I was able to pick 1920x1080 in the game itself, and it looked good and ran really well.

So the Deck is capable of running games well on 4K TVs in lower resolutions, but not in Game Mode. Unless there’s a setting I’m missing.

I’m hoping it can be fixed with software, otherwise I need to find an old 1080p only HDMI cable and use that or something.

[TiredTimelord]

It's the upscaling on the performance tab. There is no option to turn it off in game mode so it's forcing all games to try to run at 4k through upscaling which the deck is unable to do. I have the same issue and am having issues with the desktop mode since the last update this morning. They need to add a way to access performance mode with a regular controller (perhaps holding the menu button for 2 seconds?) Then there needs to be an option to turn off the upscaling as well as to choose a resolution the same way you choose in desktop mode. This will ensure you can connect up without having to fiddle with desktop mode if you don't want to and run everything from the controller.

[ka]

I found a simple solution, and it works!!!
In desktop mode, type these 3 lines on the command line:

sudo steamos-readonly disable
sudo sed -i 's/-w 1280 -h 800/-W 1920 -H 1080/g' /usr/bin/gamescope-session
sudo steamos-readonly enable

Fixed!!!

(from https://www.reddit.com/r/SteamDeck/comments/wro0s8/comment/ikua0e7/)

You can also run a script for doing this. Create a text file named "fix_hdmi.sh" with the 3 lines above.

To run the script type:
sh fix_hdmi.sh [ENTER]

sh f [TAB] [ENTER]
also works.

(or, for the Linux savvy people, just edit the gamescope-session file yourselves)


Now I can run Dirt Rally 2 on my 4k OLED with awesome picture quality and a solid 60fps.
Steam Deck HDMI output at 1080p.
LG 55BX OLED doing upscaling and sharpening.
Hard to tell from real 4k.

[Marlock]

It finally happened (in beta)! I'm going slightly maaad...

https://steamcommunity.com/app/1675200/discussions/0/3362523432278178550/

SteamOS 3.3.2 Beta Patch Notes: September 22nd, 2022

• Added external display output resolution and refresh rate selection UI in Display Settings (requires Steam Client Beta)
  
• Automatically avoid problematic resolutions like 4096x2160 or 30Hz modes on external displays