[bawolff]

I wonder why you couldn't just add a colour profile to a png file to shift the colours to this super white colour.

For that matter i thought avif supported HDR images.

[zokier]

Short answer: nobody has implemented it yet.

See https://w3c.github.io/ColorWeb-CG/#png and the linked ML thread for some details.

[londons_explore]

I think specifically mobile safari refuses to pass through the HDR properties in most cases.

I think Apple is trying to keep HDR for native apps only, like many other platform exclusive features like faceid, fingerprint reading, etc - which are all unavailable to webapps. Video is probably an exception.