I'm still confused after reading these two documentation pages.

https://docs.developers.optimizely.com/content-management-system/docs/using-notifications

https://docs.developers.optimizely.com/content-management-system/docs/usage-examples

I've implemented the:

private static readonly INotificationUser NotificationSender = new NotificationUser("SystemNotificationSender");
public const string NotificationChannelName = "ExecutableJob.Invoke.Process";

await _notifier.PostNotificationAsync(new NotificationMessage
{
    ChannelName = NotificationChannelName,
    Subject = broadcasted.Subject,
    Content = broadcasted.Message,
    Recipients = new[] { new NotificationUser(broadcasted.UserName)  }, // Logged in User
    Sender = NotificationSender,
    TypeName = "OnStatusChange"
}

and in startup:

var optionsRegistry = app.ApplicationServices.GetRequiredService<INotificationChannelOptionsRegistry>();
optionsRegistry.Add(...NotificationChannelName, new NotificationChannelOptions(true));