In this thread https://docs.mongodb.com/realm/sdk/dotnet/quick-start-with-sync/#initialize-the-app you wrote :
app = App.Create(myRealmAppId);
This is wrong. UWP and WPF by default has App class, and it doesn’t have any Create method. And both Realms and Realm package doesn’t have Realms.App or Realm.App too. So what’s the App class you referenced?
The documentation should be detail and it’s much better if you have demo project for .NET since your document is really vague.