No refresh on text changed on uno platform

MainPage.xaml

<Page
    x:Class="UnoTest1.MainPage"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="using:UnoTest1"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    mc:Ignorable="d"
    x:Name="Page">

    <Grid Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">
        <StackPanel HorizontalAlignment="Stretch" >
            <TextBlock x:Name="TextBlock1"
                Text="{Binding TbText}" Margin="20" FontSize="30" 
                       HorizontalAlignment="Center"/>
            <Button HorizontalAlignment="Center"
                    Margin="24"
                    MinWidth="200"
                    Height="48"
                    Click="ButtonBase_OnClick"
                    Content="Mega button"></Button>
        </StackPanel>
    </Grid>
</Page>

MainPage.xaml.cs

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.IO;
using System.Linq;
using System.Reflection;
using System.Runtime.CompilerServices;
using System.Runtime.InteropServices.WindowsRuntime;
using Windows.Foundation;
using Windows.Foundation.Collections;
using Windows.Storage;
using Windows.UI.Xaml;
using Windows.UI.Xaml.Controls;
using Windows.UI.Xaml.Controls.Primitives;
using Windows.UI.Xaml.Data;
using Windows.UI.Xaml.Input;
using Windows.UI.Xaml.Media;
using Windows.UI.Xaml.Navigation;

#if __IOS__

using AVFoundation;
using Foundation;

#endif

// The Blank Page item template is documented at http://go.microsoft.com/fwlink/?LinkId=402352&clcid=0x409

namespace UnoTest1
{
    public class ViewModel : INotifyPropertyChanged
    {
        private string _tbText = "THIS IS TEXT";

        public string TbText
        {
            get => _tbText;
            set
            {
                _tbText = value;
                OnPropertyChanged();
            }
        }

        public event PropertyChangedEventHandler PropertyChanged;

        private void OnPropertyChanged([CallerMemberName] string propertyName = null)
        {
            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
        }
    }

    /// <summary>
    /// An empty page that can be used on its own or navigated to within a Frame.
    /// </summary>
    public sealed partial class MainPage : Page
    {
        ViewModel _vm = new ViewModel();

        public MainPage()
        {
            this.InitializeComponent();
            this.DataContext = _vm;
        }

        private void ButtonBase_OnClick(object sender, RoutedEventArgs e)
        {
            _vm.TbText = "Button clicked!";
        }
//            var assembly = typeof(MainPage).GetTypeInfo().Assembly;
//            var stream = assembly.GetManifestResourceStream(assembly.GetName().Name + ".Assets.collect.wav");
//#if WINDOWS_UWP
//            MediaElement mysong = new MediaElement();
//            mysong.SetSource(stream.AsRandomAccessStream(), "audio/wav");
//            mysong.Play();
//#endif
//#if __IOS__
//            var aus = new AudioService(stream);
//            aus.PlaySound();

//#endif
//        }

//#if __IOS__

//        class AudioService
//        {
//            private AVAudioPlayer _ringtoneAudioPlayer;

//            public AudioService(Stream source)
//            {
//                _ringtoneAudioPlayer = AVAudioPlayer.FromData(NSData.FromStream(source));
//                _ringtoneAudioPlayer.NumberOfLoops = 1; // infinite
//            }

//            public void PlaySound()
//            {
//                if (_ringtoneAudioPlayer != null)
//                {
//                    _ringtoneAudioPlayer.Stop();
//                }

//                _ringtoneAudioPlayer.Play();
//            }

//            public void StopSound()
//            {
//                if (_ringtoneAudioPlayer != null)
//                {
//                    _ringtoneAudioPlayer.Stop();
//                }
//            }
//        }
//#endif

    }
}