I believe that is the same behaviour that I'm looking for on that button at the home forum level page, but that button isn't available on all pages, at least not that I can see. So once you go into a thread, to use that button you'd have to back out to the home and then get the button again. Or access the menu item as I said.I have never used “what’s new”.
I just click new posts.
@sswilson same comment as to @crazyea.
Edit: Another option would be to keep that button available on all pages, but then you do have to go back to the top to see it. The top menu remains visible at all times.