Same as reddit, same as Facebook, same and Twitter. It's the same as any website. Anything you post is most certainly getting scraped to create a profile on you. Whether that is for nefarious purposes for just to better serve you ads is irrelevant.
There is no privacy to anything you post on the internet to public forums.
Just look at the effort that went into making "work from home" viable back in 2020. The fediverse is not a unique case of being a "privacy nightmare".
For fun, try to "dox yourself" by searching on Google from a different IP and computer from what you normally use for your name, usernames, etc. to see what information is freely available to the public.