WPF how to bind value to TextBox using MVVM pattern correctness

I am currently trying to use WPF. I created a demo project using Windows Template Studio for Visual Studio.

Now I want to add a textbox which should be autosaved by the MVVM pattern. I have added the following XAML in my settings page.

<TextBlock
   Style="{StaticResource BodyTextStyle}"
   Text="Default Page" />
<TextBox Text="{Binding DefaultPage}">
    <i:Interaction.Triggers>
        <i:EventTrigger EventName="TextChanged">
            <i:InvokeCommandAction Command="{Binding SetDefaultPageCommand}" CommandParameter="{Binding DefaultPage}" />
        </i:EventTrigger>
    </i:Interaction.Triggers>
</TextBox>

SettingsViewModelI added the following lines to it:

private readonly IDefaultPageService _defaultPageService;
private string _defaultPage;
public ICommand SetDefaultPageCommand => _setDefaultPageCommand ?? (_setDefaultPageCommand = new RelayCommand<string>(OnSetDefaultPage));

public string DefaultPage
{
    get { return _defaultPage; }
    set { Set(ref _defaultPage , value); }
}

private void OnSetDefaultPage(string defaultPage)
{
    _defaultPageService.SetDefaultPage(defaultPage);
}

The service to save is implemented as:

public class DefaultPageService : IDefaultPageService
{
    public DefaultPageService()
    {
    }

    public void InitializeDefaultPage()
    {
        var theme = GetDefaultPage();
        SetDefaultPage(theme);
    }

    public void SetDefaultPage(string defaultPage)
    {
        App.Current.Properties["DefaultPage"] = defaultPage.ToString();
    }

    public string GetDefaultPage()
    {
        if (App.Current.Properties.Contains("DefaultPage"))
        {
            var defaultPage = App.Current.Properties["DefaultPage"].ToString();
            return defaultPage;
        }

        return "https://google.com";
    }

}

Saving the new string works, but unfortunately my command is called before the actual bound property changes its value. I have tried many different TextBox events such as KeyUpand KeyDown. The only event I've found that works, but the GUI fires LayoutUpdatedit again and again , so I'm pretty sure there's a better way.

Does anyone know how I can fix this?