Progressive decode: JPEG vs JPEG XL vs FLIF
Image compressed to a similar perceptual quality (ssimulacra score around 0.05), encoded progressively with mozjpeg, cjxl -p, and lossy flif.
On a slow 5 kB/s connection, this is what you could see (provided the application redraws at every kilobyte, which is not what happens in reality).