There are no things like private messages on facebook.
Use pgp.
Facebook allegedly sold your private messages to Netflix, so they could see what "shows you recommend to your friends"
The more you know.
https://www.foxbusiness.com/technology/facebook-let-netflix-peek-user-dms-explosive-court-docs-claim
Discussion
I don't use Facebook 🙃
Deleted Facebook apps a long time ago. But still using meta apps like WA+IG unfortunately. Slowly moving away from those.
I'm not sure. what are you talking about. Facebook isa website, not an app, you can not uninstall a website only delete cookies and local data(fuck javascript) and never visit it anymore.
You have to protect your privacy. You can encrypt and sign your posts on facebook like on any other website allowing you tu post data.