The Task Pane is a docked area within the PowerPoint 365 for Mac interface that provides more options than dialog boxes. Also, unlike most dialog boxes which cover the Slide Area, you can view both the active slide(s) and the Task Pane at the same time. The Task Pane, therefore, provides a more streamlined experience. In fact, all the options within the Format dialog boxes from older versions of PowerPoint are now available within the new Format Task Panes in PowerPoint.
Learn about the Task Pane in PowerPoint 365 for Mac.