Can't use x:Bind with Converter in Window

Describe the bug Hi, I’ve tried to use the x:Bind with IValueConverter. But the project doesn’t compile - CS1503 Argument 1: cannot convert from 'TestApp.MainWindow' to 'Microsoft.UI.Xaml.FrameworkElement'. Please take a look at the following code. What I do wrong?

Steps to reproduce the bug

<Window
    x:Class="TestApp.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="using:TestApp"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    mc:Ignorable="d">
    <Grid RowDefinitions="Auto, *" x:Name="root">
        <Grid.Resources>
            <local:MyConverter x:Key="MyConverter"/>
        </Grid.Resources>
        <StackPanel Spacing="12"
                    Grid.Row="1">
            <TextBlock Text="{x:Bind MyProperty, Converter={StaticResource MyConverter}}"/>
        </StackPanel>
    </Grid>
</Window>

    public class MyConverter : IValueConverter {
        public object Convert(object value, Type targetType, object parameter, string language) => value;
        public object ConvertBack(object value, Type targetType, object parameter, string language) => value;
    }

    public sealed partial class MainWindow : Window {
        public MainWindow() {
            this.InitializeComponent();            
        }
        public string MyProperty { get; } = "Test";

Expected behavior

Screenshots

Version Info

NuGet package version:

[WinUI 3 - Project Reunion 0.5: 0.5.6]

Windows app type:

UWP	Win32
	Yes

Windows 10 version	Saw the problem?
Insider Build (xxxxx)
October 2020 Update (19042)	Yes
May 2020 Update (19041)
November 2019 Update (18363)
May 2019 Update (18362)
October 2018 Update (17763)
April 2018 Update (17134)
Fall Creators Update (16299)
Creators Update (15063)

Device form factor	Saw the problem?
Desktop	Yes
Xbox
Surface Hub
IoT

Additional context

[qJake]

Coming from a strictly WPF/.NET Framework background, and trying out WinUI 3.x for the first time… this is really non-intuitive, especially when trying to port multi-window applications.

I realize that there is a fundamental difference in how UWP apps behave versus how traditional multi-window applications behave, but there should be an elegant solution to this problem nonetheless.

[michael-hawker]

Yeah, I too keep getting tripped up that Window isn’t a DependencyObject… it’s a bit weird.

If the expectation that Window is supposed to just be the host like the implicit Frame created in App.xaml.cs for UWP apps, maybe the File -> New template for WinUI 3 should separate out the MainWindow as also having a MainPage class hosted by it already setup?

This would help lead developers to the proper constructs when building their app and set them up for success vs. having everyone start dumping UI in MainWindow and then getting frustrated.

I mean I really like how the MainWindow is more exposed compared to all the extra logic on Startup that was done in the UWP space, but it’s super confusing and bare-bones template when trying to start building an app from afterwards without creating a new Page first.