My forum is currently set to invite-only, mainly because I want to encourage people to create accounts to participate in discussion instead of just lurking. But now i’m wondering - will this prevent topics from being seen on Google search results?
If it invites only no it will not. Since this makes it so you need to be logged in to view content. But if it is read-only and you need to be invited to post then it will appear in google since their scrapers that don’t have an account could see the page.
You can tell Google (and other well-behaved sites) to not index or list your site. But if it is public, this won’t prevent less-well-behaved scrappers from doing whatever they want.
BTW, please note that
login required and
invite only are two different things.
Your site currently has both enabled which means that nobody without an account can see your content, be they search engines or people.
A bit offtopic now, but not tell, but ask. That difference is sometimes important to understand, because there are situations when googlebot just doens’t care of
robots.txt and will index — like when someone shares a link via gmail.