NavigationLink で遷移してから戻る場合

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presentationMode.wrappedValue.dismiss() で戻れる

 struct SomeView: View {
    @Environment(\.presentationMode) var presentationMode: Binding<PresentationMode>
    var body: some View {
        Button {
            presentationMode.wrappedValue.dismiss()
        } label: {
            Text("Button")
        }
    }
}