AVSpeechSynthesizer does not work on "Mac (Designed for iPad)", with some voices

The iOS 26 sample below speaks well on iPhone/iPad devices and the iOS simulator.

But it does not speak on "Mac (Designed for iPad)", with a voice downloaded via the macOS settings.

Instead it issues this warning :

Invalid maui voice identifier com.apple.voice.enhanced.en-US.Samantha

How to make an iOS app speak on "Mac (Designed for iPad)", with a downloaded voice ?

Note :

• I use iOS 26.5.2 and macOS 26.5.2.
• I use voices that can be found in System Settings > Accessibility > Read & Speak > System voice.
• I have checked that "Samantha (Enhanced)" is the "System voice" in the macOS settings.
• I have checked that the same issue occurs with other voices and other languages.
• There is no such issue for a voice that never needs to be downloaded.

import AVFAudio
import SwiftUI

@main
struct SampleApp: App {

    var body: some Scene {

        WindowGroup {

            SampleView()
        }
    }
}

struct SampleView: View {

    private var synthesizer = AVSpeechSynthesizer()

    var body: some View {

        Button("Speak", action: speak)
    }

    private func speak() {

        let utterance = AVSpeechUtterance(string: "I speak English.")

        utterance.voice = AVSpeechSynthesisVoice(language: "en")

        self.synthesizer.speak(utterance)
    }
}