Apple announced support for JPEG XL last year at WWDC; Apple's 1st party apps supported JPEG XL when iOS 17 shipped: https://developer.apple.com/wwdc23/10122

Regarding older hardware, I addressed that: https://news.ycombinator.com/item?id=41611709

It’s good in a corporate setting, you don’t want to suddenly have to deal with a new file format for which you won’t have an app installed on your company PCs to view them.