Using DataGrid Class (CommunityToolkit.WinUI.UI.Controls) in a XAML island from a C# Class Library

I have the following setup : I am display WinUI3 elements from a C# Class Library in a Win32 C++ app using XAML islands, the control that I want to use is a CommunityToolkit.WinUI.UI.Controls DataGrid but this is only available for C# which is why I need to use a C# Class Library.

I have this function which gets called in my Win32 app :

public static int ShowWindow(nint args, int sizeBytes)
#pragma warning restore IDE0060 // Remove unused parameter
{
    // Initialize WinAppSDK 1.6 or 1.7
    if (!Bootstrap.TryInitialize(0x00010007, string.Empty, new PackageVersion(), Bootstrap.InitializeOptions.None, out var hr) &&
        !Bootstrap.TryInitialize(0x00010006, string.Empty, new PackageVersion(), Bootstrap.InitializeOptions.OnNoMatch_ShowUI, out hr))
        return hr;

    if (_app == null)
    {
        _app = new DummyApp(); // Optional: enables WinUI 3 styles
        DispatcherQueueController.CreateOnCurrentThread();
    }

    var _source = new DesktopWindowXamlSource();
    _source.Initialize(Win32Interop.GetWindowIdFromWindow(args));

    var window = new Microsoft.UI.Xaml.Window();

    var sampleData = new List<Person>
    {
        new Person { Name = "Alice", Age = 30 },
        new Person { Name = "Bob", Age = 25 },
        new Person { Name = "Charlie", Age = 35 }
    };

    var dataGrid = new CommunityToolkit.WinUI.UI.Controls.DataGrid
    {
        AutoGenerateColumns = true,
        ItemsSource = sampleData,
        Margin = new Thickness(20)
    };

    var grid = new Microsoft.UI.Xaml.Controls.Grid
    {
        Background = new Microsoft.UI.Xaml.Media.SolidColorBrush(Microsoft.UI.Colors.White)
    };
    grid.Children.Add(dataGrid);

    window.Content = grid;
    window.Activate();

    return 0;
}

It compiles and runs except that the DataGrid doesn't show up, the window I am creating is empty, the same code works and displays the DataGrid correctly if I do this in a C# WinUI3 app. Any idea why ?

Example project in question here.