"Provided that a Third Party User is followed by or following a Threads account, Meta will ingest these pieces of data specifically:

Username, Profile Picture, IP Addres, Name of Third Party Service, Posts from profile, Post interactions (Follow, Like, Reshare, Mentions).

Granted, these sound like basic table stakes for federation to work well within the Fediverse. Most Mastodon servers collect roughly about the same amount of data for basic features to work correctly. But again, Meta is first and foremost an advertising and data harvesting company, and many people aren’t happy at the idea of being subjected to this treatment from the vantage point of their own servers."