I've reproduced the error using the provided solution, however, I wasn't able to indicate what is the reason behind it. It looks like it is something related to the .NET Core 3.1 project setup, but it wasn't clear what exactly. I've managed to resolve this by creating a new WPF User Control Library (.NET) project with Visual Studio 2019 Preview (preferably the latest version). The new project should replace the original one - DemoAll.Modules.Telerik.
I hope this helps.
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