This is a feature request, not a bug.

Detailed description
JPEG XL is a next-generation codec by JPEG Group.

ImageMagick already support JPEG XL, and libvips trying to support JPEG XL. JPEG XL decoding is also supported by Chrome Beta and Firefox Nightly.

There is a reference encoding and decoding library for JPEG XL
https://gitlab.com/wg1/jpeg-xl