just fuking use a poly fill to add support of JPEG XL. Or store JPEG XL and convert on the fly to JPEG to supply it to browsers that don't support JPEG XL.
In HTML, use `<picture>`: https://developer.mozilla.org/en-US/docs/Web/HTML/Reference/...
In CSS, use `image-set()`: https://developer.mozilla.org/en-US/docs/Web/CSS/image/image....
Doesn't a polyfill imply more Javascript running on the device?