"JPEG XL" is a little bit of a misnomer as it's not just "JPEG with more bits". It supports lossless encoding of existing content at a smaller file size than PNG and allows you to transcode existing JPEGs recoverably for a 20% space savings, the lossy encoding doesn't look nearly as ugly and artifacted as JPEG, it supports wide gamut and HDR, and delivers images progressively so you get a decent preview with as little as 15% of the image loaded with no additional client-side effort (from https://jpegxl.info/).
It is at least a very good transcoding target for the web, but it genuinely replaces many other formats in a way where the original source file can more or less be regenerated.
It is at least a very good transcoding target for the web, but it genuinely replaces many other formats in a way where the original source file can more or less be regenerated.