I haven’t dug into the test data or methodology myself but I read a discussion thread recently (on Reddit - /r/jpegxl/comments/l9ta2u/how_does_lossless_jpegxl_compared_to_png) - across a 200+ image test suite, the lossless compression of PNG generates files that are 162% the size of those losslessly compressed with JPEG XL.

However I also know that some tools have bad performance compressing PNG, and no certainty that those weren’t used