A SwiftUI NavigationStack with a custom background color and no line below the title.

NavigationStackWithoutLine.swift

struct NavigationStackWithoutLine: View {
    let backgroundColor = Color.green
    var body: some View {
        NavigationStack {
            ScrollView {
                Text("Hello, world!")
                    .frame(maxWidth: .infinity)
                    .foregroundColor(.white)
            }
            .navigationTitle("Hello")
            .navigationBarTitleDisplayMode(.large)
            .toolbarColorScheme(.light, for: .navigationBar)
            .toolbarBackground(.hidden, for: .navigationBar)
            .background { backgroundColor.ignoresSafeArea() }
            .overlay(alignment: .top) {
                backgroundColor.alignmentGuide(.top) { $0[.bottom] }
            }
        }
    }
}