Comment by EnPissant

I asked claude to investigate:

  Your Display Configuration

  Both monitors are outputting 10-bit color using the ABGR2101010 pixel format.

  | Monitor                | Connector | Format      | Color Depth | HDR          | Colorspace |
  |------------------------|-----------|-------------|-------------|--------------|------------|
  | Dell U2725QE (XXXXXXX) | HDMI-A-1  | ABGR2101010 | 10-bit      | Enabled (PQ) | BT2020_RGB |
  | Dell U2725QE (XXXXXXX) | HDMI-A-2  | ABGR2101010 | 10-bit      | Disabled     | Default    |

* Changed the serial numbers to XXXXXXX

I am on Wayland and outputting via HDMI 2.1 if that helps.

EDIT: Claude explained how it determined this with drm_info, and manually verified it:

> Planes 0 and 3 are the primary planes (type=1) for CRTCs 62 and 81 respectively - these are what actually display your desktop content. The Format: field shows the pixel format of the currently attached framebuffer.

EDIT: Also note that I am slowbanned on this site, so may not be able to respond for a bit.

EDIT: You should try connecting with HDMI 2.1 (you will need a 8k HDMI cable or it will fall back to older standards instead of FRL).

EDIT: HDR on youtube appears to work for me. Youtube correctly indentifies HDR on only 1 of my monitors and I can see a big difference in the flames between them on this scene: https://www.youtube.com/watch?v=WjJWvAhNq34