From the docs:
Using XAML Islands to host WinRT XAML controls is supported only in WPF and Windows Forms apps that target .NET Core 3.x. XAML Islands are not supported in apps that target the .NET Framework.
Judging by the format of your project file and the fact that you are still using a
packages.config file, it seems like you are targeting the .NET Framework. This is not supported.
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