Comment by llm_nerd

Kind of orthogonal, but note that JXL creation tools are still uneven. Affinity, for instance, has terrible JXL creation. I don't know what they're using, but it's glitchy, and yields horrible compression levels relative to the quality, and I know a number of people that were soured on JXL purely because Affinity is a poor source for it.

For that tool you need to output an uncompressed target and use the reference command line tools, preferably libjxl and cjxl (which is still the reference, while jxl-rs remains the experimental), to create the JXL. You will have better compression with better quality, minus the glitches.