Google Takeout guide
What the JSON beside each photo is for.
Google Photos exports information it manages separately from the original media as JSON sidecars. The filename may be truncated or use several supplemental-metadata suffixes.
Useful fields
The most useful fields include photoTakenTime, creationTime, geoData, geoDataExif, title, description, and mobile upload origin. Album folders may also contain a metadata JSON naming the album rather than a media item.
Matching is the difficult part
Long filenames may be shortened, copies may receive numeric suffixes, edited media may change names, and sidecars can land in another archive. A repair tool should prefer exact and title-based evidence and leave ambiguous guesses unresolved.
Do not delete sidecars first
Keep the original ZIPs as the immutable backup. Remove JSON files only from a verified output after dates, locations, descriptions, and album relationships have been checked.