The option to search for titles is still available for logged-in users. It was moved from the separate checkbox into the dropdown below:
But it’s missing for logged-out users:
But it seems this has been the case before, too. It’s the same on a forum that is still on v3.6.0.beta1-dev. The checkbox is only visible when I am logged in
I wonder why only users who are logged in can see this option. I think it would make sense to show it for visitors, too.