Not every platform contains uses 1:1 for their product ads. You can adjust the size of your canvas!
Change Placement Size
Each design template will only render out in the current placement size of the canvas. To change your canvas size, go to the upper right of your toolbar and select the size from the platform in which you intend to run your DPA.
Now that you've adjust the size of your artboard, you can begin designing for the platform you want to run on.
One Placement Per Design
Each design can only hold one placement size. If you want to use the same design template for a different placement size, simply clone the design and change the placement size in the newly cloned design template.
For channels like Meta, you can add each design into its own treatment slot, allowing you to then assign multiple sizes to one ad