Does a Photo Metadata Fixer Need an Internet Connection?
What actually requires the network, and what does not.
Reading .json files and writing dates into photos is pure local work. It needs no network at all, and a tool that insists on one for that is doing something you should ask about.
One feature genuinely does need the internet: turning GPS coordinates into place names like Vienna or Lisbon. That looks up the coordinates in an online service, and it is optional.
Takeout JSON Metadata Fixer works with the network off. Only place-name lookup needs a connection, and you can leave it switched off. Your photos never leave your computer either way.