private PwmPin buzzerPin;
private PwmController pwmController;

public RainbowHAT()
{
    // ... do something else
    InitAsync();
}

private async void InitAsync()
{
    Logger.Log(this, "Init");

    // Setup PWM controller.
    if (LightningProvider.IsLightningEnabled)
    {
        LowLevelDevicesController.DefaultProvider = LightningProvider.GetAggregateProvider();
    }

    var pwmControllers = await PwmController.GetControllersAsync(LightningPwmProvider.GetPwmProvider());
    if (pwmControllers == null || pwmControllers.Count < 2)
    {
        throw new OperationCanceledException("Operation canceled due missing GPIO controller");
    }

    pwmController = pwmControllers[1];
    pwmController.SetDesiredFrequency(50);

    // Setup buzzer
    buzzerPin = pwmController.OpenPin(13); <-- CRASH
    buzzerPin.SetActiveDutyCyclePercentage(0.05);
    buzzerPin.Start();
}