How Func<T,TResult> works in a ReactMethod?

Hello, I just want to ask a question about how Func<T,TResult> works as an argument in a ReactMethod. I know we have Action<T> and it works well as a ReactMethod argument, but Action only works for void functions and I need to capture the returned value.

This is my C# code:

[ReactMethod("sampleFunction")]
public void SampleFunction(string sample,  Func<JSValueObject, JSValue> handler)
{
   var obj = new JSValueObject()
   {
       { "sample1", "sample1" },
       { "sample2", "sample2"},
       { "arguments", "arguments"}
   };

   JSValue result = handler(obj);
   Console.WriteLine(result);
}

And this is my Typescript code:

const getCallback = function() {
    return function(result) : string {
      console.log(result.sample1);
      return "thank you";
    };
};

NativeModules.SampleModule.sampleFunction("sample", getCallback());

Actually, I cant build my project because I getting this error in my SampleFunction:

If it helps, the error happens in line 46.

How I can fix this? Also, my Js call is correct?
Thanks in advance :)

My react-native and react-native-windows versions:
"react-native-windows": "0.64.6",
"react-native": "0.64.1"

Start with the C# SampleFunction ReactMethod and the TypeScript NativeModules.SampleModule.sampleFunction call, then reproduce the build error reported at line 46 using React Native Windows 0.64.6. Done means determining whether this callback signature is supported and identifying the correct supported call shape, with the build error resolved.