SwiftUI - TextField - Clear value of type Double on focus, restore on deselect

Scenario:
In SwiftUI, my TextField has a Double value. On tapping/focusing the TextField the current Double value is cleared, to allow the user to easily enter a new value without having to select and delete the current value. If the user does not enter a new value, the old value is restored on deselect.

Issue

Utilising .focused() and .onChange(of:) this does not appear to be possible. Below code correctly clears the value (visible in console). However, the change is not reflected within the UI. Forcing the UI to update by utilising .id() on the TextField deselects the TextField, making this workaround useless.

Why does the UI not update from the change to the TextField value property?

struct ContentView: View {
    
    @FocusState var focus: Bool
    @State var test: Double? = 100
    @State var id: UUID = UUID()
    
    var body: some View {
        VStack {
            TextField("Placeholder", value: $test, format: .number)
                .id(id)
                .focused($focus)
                .onChange(of: focus, perform: { editing in
                    var oldValue: Double? = test
                    if editing {
                        self.$test.wrappedValue = nil
                        self.$id.wrappedValue = UUID()
                    } else {
                        if test == nil {
                            self.$test.wrappedValue = oldValue
                            self.$id.wrappedValue = UUID()
                        }
                    }
                })
        }
        .padding()
    }
}

Is there a way to do this with SwiftUI's TextField?