MainPage.xaml

<Page
    x:Class="FilePickerMultiContextTest.MainPage"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    mc:Ignorable="d"
    Background="Black"
    RequestedTheme="Dark">

    <!-- Root grid -->
    <Grid Padding="56">
        
        <!-- Header-->
        <StackPanel Spacing="8">
            <TextBlock Text="FileOpenPicker Workaround for Xbox MUA" Style="{ThemeResource TitleTextBlockStyle}" TextAlignment="Center" />
            <TextBlock Text="This sample explains how to fix the 'Invalid Window Handle' issue when trying to show a FileOpenPicker that was created with CreateForUser, on a MUA." TextWrapping="WrapWholeWords" TextTrimming="None" TextAlignment="Center" HorizontalAlignment="Center" Opacity="0.7" />
        </StackPanel>
        
        <!-- Items -->
        <StackPanel Spacing="12" VerticalAlignment="Center" HorizontalAlignment="Center">
            <Button x:Name="TestPickerButton" Content="Open a File Picker (Multi-user)" HorizontalAlignment="Center" />
            <TextBlock x:Name="StatusText" Text="" HorizontalAlignment="Center" Opacity="0.7" />
        </StackPanel>
    </Grid>
</Page>