I tried the ACR installer from that linked page. I could not find an uninstall option, so I ran it as an installer, perhaps writing over the existing version 16.5 files (or leaving them in place). Then I rebooted and tried a test, editing a D850 NEF raw file, exporting to HDR AVIF. Same result as before: the file renders as SDR in Photoshop, Chrome, GraphicConverter, etc.
I compared the metadata from two files, both edited from the same D850 raw file, with the same settings, and saved as HDR AVIF. One was previously done in ACR 16.4, the other in ACR 16.5. I viewed the data with the ExifTool feature of GraphicConverter, transferred the text to BBEdit and ran a diff. There were significant differences, other than what would be expected from files edited at different times.
In the file edited with ACR 16.4
Transfer Characteristics: SMPTE ST 2084, ITU BT.2100 PQ
In the file edited with ACR 16.5
Transfer Characteristics: sRGB or sYCC
In the file edited with ACR 16.4, there were additional metadata for HDR
Max Content Light Level:
3248
Max Pic Average Light Level:
63
---- XMP-hdr ----
CCV Primaries XY:
0.6799,0.3200,0.2650,0.6900,0.1500,0.0600
CCV White XY:
0.3127,0.3290
CCV Min Luminance Nits:
0.005929
CCV Max Luminance Nits:
3247.784141
CCV Avg Luminance Nits:
62.910562
Scene Referred:
False
In the file edited with ACR 16.5 those HDR metadata were absent
At this point, I don't know what else I can try, other than a complete uninstall and reinstall of all Adobe files, which can be messy.
