

It’s unclear why Google stuck with PNG for HDR screenshots instead of a format supported by Ultra HDR such as JPEG.
Because for good lossless HDR you’ve got a grand total of 2 options, PNG and JPEG XL. And Google don’t want people to know of yet another use case for JXL.
They really want to promote their AVIF format, and supporting JXL would hinder that (Since JXL is a much nicer upgrade path from JPEG/PNG than AVIF is)
Like you can transparently go from JPEG to JXL and back with no loss, which isn’t possible with AVIF. And PNG to JXL gives you a smaller file, while it’s usually the opposite with AVIF (Unless you get lucky, as lossless AVIF can be beaten by a BMP in a ZIP file). There’s also the issue of speed, AVIF is slow to encode compared to other formats (And while hardware decoding is possible, it’s also geared towards video, so the quality is often lacking, and can sometimes be slower than plain software encoding)