Recognize watchOS10 finger double-tap gesture

Apple Watch Ultra 2, watchOS 10.2

I'm trying to recognize a finger double-tap gesture in watchOS 10.2 on an Apple Watch Ultra 2 or Apple Watch 9. Apple indicates watchOS will invoke primary watch button of app, but I don't know how to specify button as primary. I've written two small watchOS 10.2 SwiftUI apps to demonstrate the problem. Does anyone see what I'm missing, or can point me to relevant docs?

APP #1 - simple one-button tap app. Touching button works, but double tap finger gesture seems recognized by watchOS as blue finger icon appears on top of watch display, shaking back and forth indicating it doesn't know what to do, but doesn't invoke Say Hello button.

import SwiftUI
struct ContentView: View {
    // Controls whether You did it message is shown
    @State private var showingSuccessMessage = false
    var body: some View {
        VStack {
            Button("Say Hello") {
                // This closure is the primary action for the button
                showingSuccessMessage = true
                // After 3 seconds, hide the success message
                DispatchQueue.main.asyncAfter(deadline: .now() + 3) {
                    showingSuccessMessage = false
                }
            }
            // Toggle the visibility of the success message
            if showingSuccessMessage {
                Text("You Did It")
            }
        }
        .padding()
    }
}
#Preview {
    ContentView()
}

APP #2 - basically same app with tap gesture recognizer. Single touch of text works, but double tap gesture while seemingly recognized by watchOS as blue finger icon appears on top of watch display, shaking back and forth indicating it doesn't know what to do, also won't invoke a touch of the Say Hello text.

import SwiftUI
struct ContentView: View {
    @State private var showingSuccessMessage = false
    var body: some View {
        VStack {
            // The view that responds to the tap gesture
            Text("Tap to Say Hello")
                .padding()
                .background(Capsule().fill(Color.orange))
                .foregroundColor(.white)
                .onTapGesture {
                    // The action to perform on tap
                    showingSuccessMessage = true
                    // After 3 seconds, hide the success message
                    DispatchQueue.main.asyncAfter(deadline: .now() + 3) {
                        showingSuccessMessage = false
                    }
                }
            // Toggle the visibility of the success message
            if showingSuccessMessage {
                Text("You did it")
            }
        }
    }
}
#Preview {
    ContentView()
}