Click Unread, then there is a Dismiss button, shown roughly in position 3. Click that, then you can dismiss tracking or unread messages (forget the exact wording).
Thank you. I’ll try this the next time that there is a New/Unread post.
I had noticed that topics that I officially “read” all the way to the bottom would no longer be highlighted as were the Unread topics. I’m guessing that the Dismiss button will turn off the Bold feature for all of the currently available (older) topics.