jpegxl is supported by pretty much every relevant program that deals with images. The web situation is purely because of Google's monopoly.

But exceedingly few cameras (this is the only one I'm aware of). If I had to guess it's probably encoding in software but still, it's a start.

There has to be someone else since my dad just emailed me a JPEGXL image less than 15 minutes ago. No idea on how he produced or procured it.