New posts never left. You just had to click the dot dot dot next to watched forums and watched threads.
It’s “New Threads” that are missing, although it was not called that. You used to be able to see them under the label “Recent Threads” on the sidebar, but it was removed around the same time as History was removed. It provided a list of newly created threads on the site.
Having a New Threads link next to New Posts would be very useful as I don’t know another way to see which threads have been created since it was removed from the sidebar.
PS What is the difference between New Posts and Recent Posts? I can’t figure it out.