You should never transcode lossy source files because there is generation loss in quality.

There is still a lot of reason for Apple to switch from HEIC to JXL for photos going forward since HEIC is patent encumbered so it will never see widespread use.

HEIC has a very messy patent situation around it which limits what tools work with it.

E.g. for official Windows support by Microsoft you need to buy the codec from the Microsoft App Store for $0.99

Formats that aim to be web standards should try not to be patent encumbered. There was a lesson to be learned from the Unisys debacle in the 1990s. If you don't want to reencode for the web, use a device that captures in a format that can be shared on the web.

Because you'll be hounded by patent pools and sued into oblivion if you dare to use it in your own software and aren't Apple, Microsoft or Samsung.

Think about how many images large platforms deliver every day, and the benefits of saving bits on each of them.