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.

At a minimum I would want them to display in my gallery app (currently Nextcloud memories), display in a browser,

there's a new push to support JPEG-XL in Firefox. it got a labs toggle recently so you can enable it for yourself. I think chrome has done something too.

and have native support at an OS level (i.e thumbnail previews). Neither format comes close to this.

what OS do you use? KDE flavoured linux handles it fine. probably not KDE specific though.

Which distro are you using?

My NAS is running Arch (btw) and I have Immich installed baremetal because someone's nicely maintaining it in the AUR... would need a little work to convert that script into something for another distro...