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.
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.