Latest activity seems to be self explanatory. And it meets my expectation of the name. New Post has me confused. I see the most random new and old stuff pop up there. When I see New Post on a forum, to me, that should mean a new thread has been started. Something different to see. Even if New Post is suppose to have some other purpose, it would be nice to had a New Thread link where all the threads on the forum are chronologically listed. When you open the link, you can see any new topics.
Posts are contained under the headings of threads. A post (a message), is not a topic, it is not a thread, although it can be about a topic. New Post does not necessarily mean a new thread.
However, instead of having a separate link to view New Threads, the forum software shows both new posts and new threads under the link heading of New Posts. Seems straightforward to me.
Having an option to view all threads, or the last N days of new threads, chronologically could be a simple SQL query. A question is cost and utility versus the need for such. You could ask if people need a New Thread option and why?
While I only click on “New Posts”. “LA” shows way too many lines of activity that I don’t care for including people’s reactions to posts. They serve different preferences.