The HDR function was working properly yesterday but, today, I'm getting the exclamation mark error message. When I click on it, a window opens showing three green dots so I don't understand what the problem is.

Hi ​@Paul25566638hra7,

Thank you for the detailed description. That's an unusual situation where the exclamation-mark warning persists even though all three compatibility requirements (HDR display, Windows HDR setting, GPU acceleration) show green. Since everything checks out on the requirements side, the issue likely lies in the display handshake or session state between Lightroom and your GPU/display pipeline.
 

Here are some targeted troubleshooting steps:

1. Toggle Windows HDR off and back on, then restart Lightroom. Go to Settings > System > Display > HDR, turn it off, wait 10 seconds, turn it back on, and then restart Lightroom. This forces a fresh HDR display handshake, which can resolve stale-state issues that accumulate between sessions.

2. Since this was working yesterday, check whether Windows auto-installed a GPU driver update overnight. If you find a recent update, try rolling back to the previous driver version to confirm.

3. Confirm Lightroom's window is on the correct monitor (if multi-display). If you use more than one monitor, Lightroom checks HDR capability on the display it's currently rendering to. Move the Lightroom window fully onto your HDR-capable display, then toggle HDR editing off and back on.

4. Does the warning appear on all photos, or only certain ones? HDR editing mode is fully supported only for HDR-capable files (HDR merges, gain-map DNGs, and supported HDR formats like AVIF/JPEG XL). If you're seeing it on standard SDR files with the HDR toggle enabled, the warning may be indicating a file-level limitation rather than a system one.

5. Windows can silently disable HDR output when on battery power or in a power-saving mode. If you're on a laptop, could you make sure you're plugged in and that your power plan isn't suppressing HDR?

6. Please check screen brightness. If you crank the screen brightness all the way up, you reduce the headroom HDR uses. Your SDR highlights will already be (almost) the maximum brightness of the screen, so there is no extra headroom for HDR highlights.
 

A couple of questions that would help narrow this down:

• Are you using an internal laptop display or an external monitor? If external, is it connected via HDMI, DisplayPort, USB-C, or through a docking station?

• Do you have multiple displays connected? If so, is Lightroom's window fully on the HDR-capable one?
   

If none of the above resolves it, I'd recommend going to Help > System Info in Lightroom, copying that information, and sharing it here.

Best,
Anshul Saini