But aren’t jpegxl and webp meant for completely different uses? Like jpeg and png are. Jpeg is better for photos and png for graphics.

No. JPEG XL is designed to be better at pretty much everything than webp (which was just adapted from a video format that was designed to be really efficient at video but without touching any patents). JPEG is best at photographs at screen resolutions, and PNG is best for screenshots of computer interfaces with lots of repeated colors, and DNG/TIFF are great for high resolution and bit depth (like for professional printing and publishing, or raw image capture from the camera). JPEG XL does a good job at all of those.