HDR Output in URP requires you to enable multiple properties to work. These properties allow URP to render scenes correctly with HDR Rendering and then output the HDR values to a display.
To activate HDR output, follow these steps.
Locate the URP asset in the Project window under Assets > Settings.
Navigate to Quality > HDR and enable the checkbox to enable HDR.
Navigate to Edit > Project Settings > Player > Other Settings and enable the following settings:
Note: Only enable Use HDR Display Output if you need the main display to use HDR Output.
If you switch to a URP asset that does not have HDR enabled, URP disables HDR Output until you change to a URP asset with HDR enabled.
Note: When HDR Output is active the color grading mode is HDR by default, even if a different Color Grading Mode is active in the URP asset.