Fediverse ≠ Signal.
This is Social Media.
If your posts are set to public, you should have exactly 0% sense of privacy here.
There's 20,000+ instances with more every single day that could be doing anything they want with your posts.
Furthermore, if you're on Mastodon, your account has an RSS feed attached that someone could be reading, completely without your knowledge.
Fediverse isn't some sort of safe haven for privacy. Not sure where that idea came from, but it's completely false.