Unread Content means new items and new comments/reviews, in your case, topics and posts.
Create a new stream and set only topics and choose Content items only in Show me then set it as default stream.
Doing this your members won’t know when their topics have replies (posts), unless they follow the topics or browse the forum constantly.
Not a good idea.
My advice: you should leave the Unread Content as default, which shows everything, and create streams per type and another for the members (in Ownership choose Content I started).