Uploading photos from MacOS Photos to Facebook?
You kind of answered your questions yourself. 

Never trust a proprietary extension or app, because you never know what the app is doing. Today it's normal for an app to collect all personal data technically possible. Facebook is evil. Exception is an Open Source client, where you can see the code.

To grant Facebook as little as possible data, you need to use their web interface (not app) and install essential privacy extensions and Ad blocker. See PrivacyTools for a list of recommendations.