.navigationViewStyle(.columns) doesn't work

Can you clarify what you mean by fixed Navigation View?

Anyway, you may need to define at least two columns inside NavigationView to test how .columns work.

A simple example:

struct CollectionView: View {
    var body: some View {
        if #available(iOS 15.0, *) {
            NavigationView {
                //First column
                VStack {
                    NavigationLink(destination:
                        //Second column replacement
                        Text("Hello")
                            .navigationBarTitle("Hello")
                    ) {
                        Text("To hello")
                    }
                }
                    .navigationBarTitle("List", displayMode: .large)
                //Second column
                EmptyView()
            }
            .navigationViewStyle(.columns)
        } else {
            // Fallback on earlier versions
        }
    }
}