@knezi @jwildeboer Quite a lot of the metadata isn't really. They can scrape obvious interactions like if you respond do a post, but not much else. Most instances don't let anyone but the poster see who actually clicked "favorite" for example. They'll see boosts, but that's about it.
More importantly, they can't see the other, less obvious stuff. For example, Facebook and Twitter know if you click to open a post, but Mastodon won't tell third parties about that.