Can you only create round shapes on the canvas? In Prezi Classic you could chose for rectangle and round frames. The rectangle frames could be set bij the screen ratio (16:9 or …). I don’t’see the rectangle options.
Currently, there are only round frames as topics in Prezi Next. Please note though that you can edit their covers and replace them with images or shapes of your preference. For further details, please check out this article in our Knowledge Base.
As for the subtopics, those can either be planets or stacks, the latter one is a rectangle shape.
I hope it helps!