SwiftUI double navigation bar

Remove the NavigationView from SecondView.

The NavigationLink puts the second view inside the first views navigations view, so you do not need to put it inside a second one.

You can still update the title of the view from SecondView like so:

struct SecondView: View {
   var body: some View {
       Text("My View")
       .navigationBarTitle("Second View")
   }
}

Quinn is right. but if You don't want a big area above:

add:

struct SecondView: View {
   var body: some View {
       Text("My View")
        .navigationBarTitle("Second View", displayMode: .inline)
   }
}