Previous code triggered obsolete warnings during compilation when someone used libjxl snapshot newer than libjxl 0.6.1
Many people use already newer, unreleased libjxl. For example Gentoo Linux doesn't have the old libjxl 0.6.1, because that version is complicated from maintainer's perspective. See https://packages.gentoo.org/packages/media-libs/libjxl
Old code didn't always work with newer libjxl. Especially lossless (quality=100) images with 16bit failed to save.
My intention is to support both old and very new libjxl.