Windows Universal App Development Template Load error

I had the same issue on Windows 10 in VirtualBox.

You must run the visual studio installer again. Select "Modify" in the Installer. Select Features > "Windows and Web Development" > "Universal Windows App Development Tools" > Click Update / Install.

Now you will be able to use the vs project template Windows IoT Core.

If such an error came up upon a project from a DirectX project template then make sure you have the UWP workload installed (from Visual Studio Installer).