How Do I Stop My Photos Being Uploaded to the Cloud?
Keeping a photo library entirely on your own machine, and what to check in the tools you use.
Turn off backup and sync in whichever app is doing it. On Android that is inside Google Photos settings. On iPhone it is iCloud Photos. Both will warn you that photos may be removed from the device, so make a local copy first.
The harder part is the tools you use afterwards. Many web-based photo fixers and converters upload everything you give them. Your holiday photos, with GPS coordinates in them, end up on somebody else's server.
Takeout JSON Metadata Fixer never sends anything anywhere. It runs on your computer and works with no internet connection at all. The only optional online step is looking up place names, and you can leave that off.