Isn't a Xamarin.Forms UWP app targeted to use .NET Core?

I am implementing Dropbox API. I succeeded in both Android and iOS. But in UWP the app is crashing after entering credentials. I see the following two lines in Output window. Isn't Xamarin.Forms.UWP app configured to use .NET Core? If not how can I set it?

Actually after entering the credentials, it asks "Do you want to switch apps". It hangs if I say NO and crashes if I say Yes. I am using "com.companyname.appname:/oauth2redirect" as the Redirect URI and UWP Package Name is set to "com.companyname.appname".

The target process exited without raising a CoreCLR started event. Ensure that the target process is configured to use .NET Core. This may be expected if the target process did not run on .NET Core.
The program '[26140] WWAHost.exe' has exited with code 1 (0x1).