From what I understand, the official questions are not available in the
forum quiz.
You can filter for official questions in the
question banks and select the difficulty levels you want as well.
Also, what tends to be the most effective practice approach is to do questions one at a time, checking your answers to each one so that you can apply what you learn in answering one question to answering the next questions you do. So, practicing with sets produced by the question banks feature works quite well.
For more detail on how to practice effectively, see these posts.
How to Score 705+ on the GMAT How to Ace the GMAT Using the Streaks Method