JPEG XL is one of the most modern image formats (in addition to AVIF). It newer and not yet as common as AVIF but it is the only image format which has practically no limitations (it supports almost everything). Compression efficiency is as good as AVIF (except for certain very low filesize settings) and it is also open source and royalty free. Encoding speeds are 3-5x faster than AVIF why it might be better for certain scenarios.

Browser support is a bit lacking at the moment so if support were added there should be automatic conversion to some more supported format (such as webp, avif or jpg) until browser support is solid (which could take anything between 2-5 years).

Apple has already embraced it. In addition of using JXL in RAW image compression it has some degree of JXL support (not sure if it extends to Safari. Adobe has also embraced it.

In addition of being efficient lossy compression algoritm which can drop sizes of JPG files with 50-75% it has a feature where you can recompress JPG files without any mathematical loss (uncompressing such JXL file is identical to original) and save 20% of space. For most users it is not large saving but for those with large image libraries even that 20% can make difference.