In a SwiftUI three split navigation view on iPad, how to check if the primary is folded?

In UIKit, I believe we can check if the split view controller primary view is in collapsed state...but can't figure out a way to check if the primary view is collapsed in SwiftUI

I tried using the horizontalSizeClass == .regular check in the secondary view...but it is always .regular for the secondary view on an iPad.

Any pointers will be deeply appreciated