How Do I Fix Google Takeout Photo Dates on a Mac?
The full process on macOS, from unzipping the export to checking the result in Finder and Apple Photos.
The order matters on a Mac, because importing into Photos first makes everything harder.
Start by unzipping every part of your export into one folder. Do not unzip them into separate places: a photo and its .json file often land in different parts, and they need to be together. Then check your Mac's timezone under System Settings, since the sidecar timestamps are UTC and get converted using whatever your machine is set to. Set it to where most of your photos were taken.
Now fix the metadata, and only then import into Apple Photos. Doing it the other way round means correcting dates by hand inside Photos, or deleting the import and starting again with forty thousand files.
The app is on the Mac App Store. Point it at the unzipped folder, choose an output folder, and let it run. It writes the real capture date, time and GPS into each photo and sets the file dates to match, so Finder sorts correctly and Apple Photos builds a proper timeline with working Memories and a filled-in Places map. Check a few in Finder with Get Info before importing everything. It runs entirely on your Mac with nothing uploaded, and the first 500 photos are free.