For the next few months at least, it looks like JPEG XL is just going to be one of those formats for Apple users, like HEIC. With people complaining about programs not supporting WEBP all the time, JPEG XL isn't going to gain much popularity in the mainstream either.
At least people supporting Safari will be able to make use of the format for faster load times soon; the <picture> element makes the transition quite painless after all.