No. iOS switched to squircles because their product designers use squircles[0]. If you extrude a rounded rectangle you get a shape that has harsh breaks in the

No. iOS switched to squircles because their product designers use squircles[0]. If you extrude a rounded rectangle you get a shape that has harsh breaks in the highlights at the point where the rounded part meets the rectangle part. To smooth this off you need a curve where the tangents are smooth. This is also known as "C2 continuity", and you get that level of continuity by ensuring that the second derivative (acceleration) of the curve has no gaps between points. Absolutely none of these properties matter for icons, of course. [0] Or at least some curve with similar tangency properties.