Beyond Mastodon and GoToSocial, every other fediverse project treats posting to public as opting in to search and indexing.
Yeah. And I think more or less that's fine. The internet isn't private. Most of us have been on the internet long enough to remember when there was absolutely zero facade of privacy online. That's just the reality of things. Be mindful of the information you volunteer and post.
Fwiw, Misskey does provides tools to deny indexing no matter what. However, these could be simply ignored by an individual or a search engine or a bot. You kinda have to trust that your wishes for not being indexed will be respected.
Otherwise, your alternative is, of course, non-public instances and/or posting private only.