For all practical purposes we can consider circle as a regular polygon with more than 22 sides.

for a polygon you need minimum three sides.

Figma does a fine job of considering shapes as polygons. so as you increase the number of sides in the polygon, it always starts at the bottom edge and then draws from there.

this transformation gives you an idea https://www.loom.com/share/4cb5177d5a6c47ccad386a5ff8e35980