Unless you opt out via robots. Mastodon has a setting that causes robots configuration (I believe via meta tag or http header) to request robots not to read the user's profile nor pages that correspond to their posts.
That's obviously suboptimal, because those posts will likely get indexed on pages of posts they are a response to. (Possibly also on "remote-viewing" pages on another Mastodon instance, but I don't know whether those are robot-excluded always and would anyway expect that to be something that's not shown in search results due to its typical uselessness -- it's usually a copy of an available primary source after all.)