Morph performs the transformation if there is the same object with different parameters on different slides. Therefore, if there is a square on the first slide, and there is a circle on the next one there will be no transformation since these are two different objects.

If you move the yellow slider of a rounded rectangle (standard shape in PowerPoint), you can get three shapes from one object. It should be rounded rectangle, not regular rectangle.

The same rectangle on different slides, with different rounding.