Yes, Safari 17 supports JPEG XL. On macOS Sonoma, macOS Ventura and macOS Monterey, as well as iOS, iPadOS, watchOS, and soon, visionOS.

We also added HEIC — especially for web apps that want to let users edit photos directly from the camera.

https://webkit.org/blog/14205/news-from-wwdc23-webkit-features-in-safari-17-beta/#images