so there’s a new search engine for the fediverse: https://search.social.
most people probably don’t expect their public posts to be searchable, especially if they use mastodon, so here’s how to opt out (for mastodon): open your settings and go to Preferences > Other, then check “Opt out of search engine indexing”.
if you’re an instance admin, you can opt your entire instance through robots.txt. you can set this up in nginx: https://stackoverflow.com/questions/1090823/how-do-i-configure-nginx-to-redirect-to-a-url-for-robots-txt-sitemap-xml#3746344