I mean, even the tooltip reflects this confusion:
It’s really “topics created in the last few days or tracked topics with unread posts.” These things just don’t make sense to unify to me!
The language and behavior of “new topics” makes sense to me. The behavior of “new replies” does not, especially when paired against (and intermingled with!) “new topics.”
I get that the current language is confusing as well, and I definitely appreciate that you’re trying to make it better. I just don’t find this better.
Really all of “Latest” “Hot” “New (15)” and “Top” are implicitly "____ topics". What I think would make most sense would be to have a “Tracked (3)” there. Clicking tracked would (by default) only show you those three tracked/watched topics containing unread posts, but there could be a toggle to show all tracked/watched topics (potentially even detangling tracking vs. watching). I’d actually really love that ability!
I know you don’t like using “Tracked” to mean both tracking and watching, but in my mental model watched topics are tracked topics with harder notifications. In fact the “Tracking” user preferences sheet combines newness, tracked, watching, and even muting. I don’t think newness belongs there; that makes more sense as the persisted state of a selector on /new itself, but that’s all a bit aside.
I suppose I could get used to something like “New (15/1)”, but that seems quite advanced.