But what I had suggested was “Unanswered”, not “Solved/Unsolved”.
The latter requires the OP to mark any response to his topic as the “solution” so that it is moved from “Unsolved”->“Solved” status, which most do not do. Hence it is very likely that even answered topics fall under “Unsolved”.
The former helps to find orphaned topics which doesn’t even have one reply.
Thanks for the clarification. This should be possible, if you use the advanced options, leave the search box empty and select “Where topics - have zero replies”: