The header image I see is indeed an AVIF but it depends on what your browser sends in the `Accept` header. Chrome sends image/avif,image/webp,image/apng,image/s

The header image I see is indeed an AVIF but it depends on what your browser sends in the `Accept` header. Chrome sends image/avif,image/webp,image/apng,image/svg+xml,image/*,*/*;q=0.8 but if you drop image/avif from there you get a webp and if also drop image/webp from the header you finally end up with a jpeg. However if you manually request that image with a custom `image/jxl` at the start of the `Accept:` header, you get a JPEG XL result. So GP is correct, but you won't see that behavior except on their PC (errr, Mac) -- unless you use Firefox and enable JPEGXL support in about:config, of course.