The Classic AceProject interface, although feature-rich, does not include an intuitive way to display and filter tasks easily. The New interface was conceived to be more performant and include powerful retrieval and filtering capabilities. In addition, a number of new views such as Boards, Charts, History, and Reports provide even more ways to interact and gain more insights into your projects and tasks.
The transition to the New interface will not happen quickly. More features are added continually. Until you can find all that is needed in the New Interface, use the button at the top to seamlessly switch between the Classic and New Interfaces.
For more information on the New Interface check out this dedicated page: New Interface Tour