The XAML Previewer has been deprecated in Visual Studio 2019 version 16.8 and Visual Studio for Mac version 8.8, and replaced by the XAML Hot Reload feature in Visual Studio 2019 version 16.9 and Visual Studio for Mac version 8.9.
For now, it use the Hot Reload insead and provide a live visual tree to receive a real-time view of your running XAML code. It shows a tree view of the UI elements of your running Xamarin.Forms application.
When you debug you project, by default, it appears on the IDE's left. If you don't see it, use Debug > Windows > Live Visual Tree to show it.
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