Although I have a post in the section that was split to make the new thread, it wasn't in my watched threads list. (I have been using the watched threads list, and today decided to look at the bell icon and it's there that I learned the new thread existed.)
So I went to the new thread and in the top right I saw the [watch] button, indicating that I wasn't subscribed.
So I went to the new thread and in the top right I saw the [watch] button, indicating that I wasn't subscribed.