SwiftUI NavigationView adds (extra) blank space on top

I'm working on a simple app (new to SwiftUI) and having some issues with the NavigationView element. I have added a NavigationView to my top-level view but this creates a block of blank space above the view that I can't seem to remove. If I take out the NavigationView the rest of the views display as expected. I have tried removing the navigation bar Title modifiers from deeper in the app but that also hasn't had any effect. I'm at a bit of a loss as to what is going on here ... have I made this too complicated for my own good? (images to illustrate the results)

Code for the view with the issue.

   
  var body: some View {
    NavigationView {
      VStack{
        todayView()
        categoryList()
        .padding(5)
        Spacer()
      }
    }
    .navigationBarTitle("")
    .navigationBarHidden(true)
  }
}

initial navigationLinks are in the categoriesList (Red) which lead to a list of items also with navigationLinks (code below)

  @EnvironmentObject var modelData: ModelData
   
  @State private var showHotListOnly = false
   
  var filteredHotTasks: [Task] {
    modelData.tasks.filter { task in
      (!showHotListOnly || task.isHotList)
    }
  }
   
  var body: some View {
    //NavigationView {
      List {
      ForEach(filteredHotTasks) { task in
        NavigationLink(destination: TaskDetail(task: task)) {
          TaskRow(task: task)
        }
      }
    }
      .navigationTitle(showHotListOnly ? "Hot List" : "Tasks")
      .navigationBarTitleDisplayMode(.inline)
      .navigationBarItems(trailing:
                  Button (action: {
                    showHotListOnly.toggle()
                  }) {
                    Image(systemName: showHotListOnly ? "flame.fill" : "flame")
                    .foregroundColor(showHotListOnly ? Color.orange : Color.gray)
                  }
                   
      )
  //}
}

Any and all help greatly appreciated! Especially before I go bald from frustration.