If you make a group and set the roundness of its borders you get something that’s not a perfect rectangle. If you set the roundness to half the width/height you get a circle. The group’s hover and click detection respects the rounded borders and only registers the mouse’s hover/click inside the curved border, not just inside the group’s overall rectangular bounding box.
It doesn’t look like it’s perfect. There are a few areas around the curved border where the mouse seems to register slightly outside of the curve, but it’s pretty good.