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XAML Previewer was removed in VS
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. Learn more about XAML Hot Reload in the documentation.
You can see this official article.
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