WinUI 3 controls in Simple Island App are invisible until focused

Building and running the unmodified Simple Island App project results in a window that looks like this:

However, there are suposed to be WinUI 3 controls on the top and bottom of the WebView2. The XAML has:

    <Grid Padding="10">
        <Grid.RowDefinitions>
            <RowDefinition Height="50"/>
            <RowDefinition Height="*"/>
            <RowDefinition Height="50"/>
        </Grid.RowDefinitions>
        <StackPanel Orientation="Horizontal" Grid.Row="0">
            <Button x:Name="Button" Click="ClickHandler">Click Me</Button>
            <TextBox Text="Text goes here" Margin="10" />
        </StackPanel>
        <WebView2 Grid.Row="1" Source="http://bing.com" />
        <Button Grid.Row="2">Last Button</Button>
    </Grid>

So there are supposed to be a Button and TextBox above the WebView2, and another Button below it.

If you click where the TextBox control is supposed to be, it shows up:

But then if you click away from it, it disappears again.

I'm using Windows 11 23H2, Windows 11 SDK 10.0.22000.0, Visual Studio 17.8.1, and Windows App SDK 1.4.3 (1.4.231115000).

Start by running the unmodified Simple Island App and inspect the XAML layout containing the StackPanel, WebView2, and bottom Button. Confirm the controls are present but invisible until focused, then verify that they remain visible after focus moves away on the reported Windows App SDK environment.