TLDR is JPEG XL is a new standard (not related to JPEG 2000) that among other things allows lossless re-compression of JPEG images with roughly 30% space saving

TLDR is JPEG XL is a new standard (not related to JPEG 2000) that among other things allows lossless re-compression of JPEG images with roughly 30% space savings, as well as a bunch of other useful features (better progressive decompression, bigger blocks, reduced banding, higher bit-depth, etc.