I have noticed that the “new” count now includes new replies and not just new posts.
I personally was preferring the previous setting, so I could see if there were new threads (I can always go to “latest” to get both threads and overall posts.)
I’ve lost track of this change. It was first tried in 2023, and reverted, but now it’s on again and on by default for everyone. Not sure if/how it’s different, but I didn’t like it back then (when I was paying closer attention to discourse dev).
I suppose we may be able to disable it.
I was able to opt-out of this change — but unfortunately that was only temporary. The Discourse team has decided to remove this site setting and will be pushing everyone to the new new system “soon”.
I really dislike this behavior, but your preferences may vary. If you missed its temporary rollout here, you can see it in action on Meta. Perhaps we’ll be able to improve it (or regress it, rather) back to the way it was through a theme component if others find it similarly confusing.
More details at that meta link above.