Attaching any significance to being “first” on open standards is a game Apple rarely plays, but which others impose upon them because Apple’s adoption is (rightly or wrongly) seen as the most consequential and/or most newsworthy inflection point.
In the specific case of JPEG XL I think Google support will be the real inflection point: no chrome and default android support is a deal breaker for wide audience content publishers.
The ironic part being of course that Chrome used to support it way too early, but support was dropped as nobody followed. So yes, Apple support is a big deal, but not more consequential than the other actors of the pretty vast ecosystems.
