https://developer.apple.com/documentation/foundation/urlsession/3767352-data?changes=latest_minor は素の Objective-C Interop ではないと思います (そもそも元の dataTask(...) は URLSessionDataTask が帰ってくるはずなので The method itself has a void result type, because all results are delivered by the completion handler block. に引っかかりそう)