JXL is working alright for me.

As an example with a lot of dynamic range, here's a JXL:

AVIF:

Both render in my desktop and iPhone browsers, just fine. I bet at least one renders for you. And I made them from RAWs from a really old camera!

The problem is, as you say... arbitrary lack of support. As an example, I can't upload either file to Lemmy. Brand new social media software, and it doesnt' recognize JXL or AVIF as valid image types, even though they should render just fine? Most image hosts wont take JXL either, hence I had to upload them to litterbox since catbox is down!

An HEIF, on the other hand, has basically 0 support outside of Apple:

All three of these render correctly on my phone, but only the top two do on other devices.