JPEG XL: the new JPEG, if the world cooperates
JPEG XL is the actual successor to the 1992 JPEG: same picture, roughly half the size, designed to last decades. Chrome and Firefox open it, Windows is warming to it, and a long tail of software hasn’t caught up yet. If you archived photos as JXL for the space savings, at some point something will refuse one.
That’s the moment to convert back. JPGs open literally everywhere, and Image Squisher is one of very few consumer tools that reads JXL at all, let alone converts it in batches.