WPF Progrss bar stringformat {} {0}% IsDetermined

//xaml
<Window x:Class="WpfApp425.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:WpfApp425"
        mc:Ignorable="d"
        WindowState="Maximized"
        Title="MainWindow" Height="450" Width="800">
    <Grid> 
            <ProgressBar Maximum="100" Minimum="0" x:Name="progressBar"
                         Height="50"
                         IsIndeterminate="True"
                         HorizontalAlignment="Stretch"
                         VerticalAlignment="Center"/>
            <TextBlock Text="{Binding Path=Value,StringFormat={}{0}%,ElementName=progressBar}"
                       HorizontalAlignment="Center" VerticalAlignment="Center"
                       FontSize="30"/> 
    </Grid>
</Window>


//.xaml.cs
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;

namespace WpfApp425
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    { 
        public MainWindow()
        {
            InitializeComponent();
            System.Timers.Timer tmr = new System.Timers.Timer();
            tmr.Elapsed += Tmr_Elapsed;
            tmr.Interval = 100;
            tmr.Start();
        }

        private void Tmr_Elapsed(object sender, System.Timers.ElapsedEventArgs e)
        {
            Dispatcher.BeginInvoke(new Action(() => 
            {
                progressBar.Value++;
                if (progressBar.Value == 100)
                {
                    progressBar.IsIndeterminate = false;
                }
            }));
        }
    }
}