popupMenuRadius property
Border radius override value for the menu on PopupMenuButton.
When used by FlexColorScheme the boroder radius of popup menus follows the defaultRadius until and including 10 dp. After which it stays at 10 dp. If you need a higher border radius on popup menus than 10 dp, you will have to explicitly override it here. It will not look very good, the highlight inside the menu will start to overflow the corners and it is not clipped along the border radius. The underlying Widget is not designed with this high border rounding in mind, which makes sense since it does not look good with too much rounding on a small menu.
The built-in behavior in FlexColorScheme allows it to match at low inherited default radius values, but to also stay below the usable max rounding automatically at higher global default border radius values.
Implementation
final double? popupMenuRadius;