Please let someone take a look at this that is has understanding of color spaces and HDR workflows.
How to recreate: Take a Raw from any Camera and open Photoshop. Drag and drop the Raw into Photoshop and edit it in HDR mode. Make sure every format is set to HDR PQ rec.2020.
Once you have the HDR image export it to psd. Take the Exported .psd and drag it into Lighroom and enable HDR in Lightroom. Now procede to export the file with HDR to avif with export hdr enabled.
Now the issue with the exported HDR file is that it has significantly less cd/m^2 then the photo must have had in lightroom preview to nearly clip on my 700cd/m^2 HDR screen. The exported ones had numbers from 200cd/m^2 to 500cd/m^2 and were displayed by windows gallary (which supports avif and its hdr metadata) way darker then the preview looked in lightroom. It also got displayed as hdr. I tested this by making sure that the shown picture was not effected by the OS hdr content brightness slider which only makes sdr content match hdr color space and therefore only effects elements on screen that are sdr. And it did not change so it was properly read as HDR and displayed as HDR. I also have a media info Screenshot which shows the max brightness. Would be easily fixable by providing a setting for Maximum Content Light Level on export.
I do not know if this is a issue of lightroom communicating with the encoder or what but those light levels are sometimes sub sdr space and clearly wrong. And i for once also belive that it was not windows thats at fault here.
I hope that this can be solved in a future update if it is not just a quirk native to my system.
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