Actually, just found another thread that has a way easier method that doesn’t require editing any of the “.ini” files.
All you need to do is use the following launch parameters:
SteamDeck=0 %command% -dx12
Using this will make the HDR setting show up in the graphics config menu which is much more convenient.
It was kind of a pain, but I figured out how to get Tetris Effect working in HDR on the OLED. I wrote how I did it here: https://www.reddit.com/r/SteamDeck/comments/17z25y5/which_hdr_games_actually_work_in_hdr_mode_some/kb8c8ea/
Figured out how to get HDR working in Tetris Effect. Here’s a guide on how to do it:
Switch to Desktop Mode
Right-click on Tetris Effect in the Steam Library view, and select “Manage -> Browse Local Files”
Navigate to "\TetrisEffect\Saved\Config\WindowsNoEditor"
Open “GameUserSettings.ini”
Near the bottom, find “bUseHDRDisplayOutput” and set its value to “True” (first letter is uppercase).
Save those changes.
Navigate to "\TetrisEffect\Saved\SaveGames[bunch of numbers]"
Open “CONF.json”
Within the section “config2D”, change the “HDR” key value to “true” (first letter is lowercase)
Save those changes.
Inside Steam, set the launch parameters for Tetris to the following:
PROTON_ENABLE_AMD_AGS=1 %command% -d3d12
Finally, launch from Game Mode (doesn’t require Proton Experimental).
Bit late to this thread, but I just figured out how to get HDR working in Tetris Effect. Here’s a guide on how to do it:
Success --> https://imgur.com/a/AHbOPAs
Tetris Effect works if you use the fix mentioned here.
Using these launch parameters enable the HDR setting in the graphics options menu:
SteamDeck=0 %command% -dx12