afaik activitypub/fediverse doesn’t have to be fully open… there’s private messages and followers only profiles on mastodon… sure, any server admins of your followed would be able to see anything you post (and thus in this case for threads for example, if you accept any follower from threads then meta can see your stuff) but this also doesn’t grant them a license to use the content

also, bluesky will eventually be the same: it only doesn’t have those issues now because they haven’t opened up their software… it’ll have federation in the future, which means it has to be somewhat programmatically open to others