Run the check
Compare SDR and genuine HDR content from the same source.
Record the Windows HDR setting and the monitor's HDR status.
Change only one brightness or tone-mapping control, then repeat.
Read the result
Only SDR material appearing dark in HDR mode differs from a panel brightness fault.
Limits and next step
Browser test colors do not establish peak luminance or HDR certification.
Repeat the check after changing one setting or connection. Keep a record of what changed before deciding whether the device needs service.