Swiftui Textfield not updating when value changes

Question

I have a textfield on a form where user can type value, but I would also like to update the content of the textfield with a button.

Here is my code :

struct test: View {
@State private var amount: Double = 0.0

var body: some View {
    Form {
        VStack {
            HStack {
                Text("Amount EUR")
                Spacer()
                TextField("Type amount", value: $amount, format: .number)
                    .keyboardType(.numberPad)
                    .multilineTextAlignment(.trailing)
            }
            
            Text("Set MAX (999)")
                .frame(maxWidth: .infinity, alignment: .leading)
                .onTapGesture {
                    print("before tap \(amount )")
                    amount = 999
                    print("after tap \(amount)")
                }
            
        }
    }
}

When I just launch the app, the first tap on the Text updates the textfield with 999, but after it does not work anymore. The amount value is correctly updated but the textfield does not reflect the change.

Would you have an explanation ?