You might need to activate one of the composers. The default composer should be activated, but perhaps it got deactivated by you? Give that a check.
I have only just started using nodeBB so I dont know if this is already in a hidden setting, but a feature I really like using in other forums is the ability to read upto a certain post in a thread, and then just be notified on new responses to that thread (having it take me to where I left off)
At the moment the unread threads shows all new threads and not new posts to previously read threads