Thank You. I was about to post I suspect both of those images would have worked better with JXL lossless.

Curious what is the better encoder here referring to?

It's an unreleased one. There's a whole section in the article about lossless, which includes data on those images, but not this mystery unreleased encoder https://jakearchibald.com/2026/jpeg-xl-vs-avif/#lossless