JPEG XL is awesome. I got 1/8 of the size converting (very small, like 800kB) PNGs to lossless JXL.
GIMP can open them I think, but can’t save them. ImageMagick supports it obviously and so does KDE’s image library so I get previews there and whatnot.
It really depends on what you want to use them with imo, if you view them in a specific program and that supports it, go for it.