You have to adjust the brightness. The settings change when HDR is enabled. I have yet to find the optimal calibration but it looks much better once you tweak it.
For those of us experiencing the issues OP is referring to, the steam deck never switches to HDR mode on the display, you can pull up the right side quick menu on the deck and on the screen with the brightness slider there will be a logo at the top right that displays “HDR” when it is receiving and displaying HDR video
You have to adjust the brightness. The settings change when HDR is enabled. I have yet to find the optimal calibration but it looks much better once you tweak it.
For those of us experiencing the issues OP is referring to, the steam deck never switches to HDR mode on the display, you can pull up the right side quick menu on the deck and on the screen with the brightness slider there will be a logo at the top right that displays “HDR” when it is receiving and displaying HDR video