The method declarations of both CreateFolderAsync(CreateFolderArg) and CreateFolderAsync(String, Boolean) are marked as obsolete:
[Obsolete("This function is deprecated, please use CreateFolderAsync instead.")]
public Task<FolderMetadata> CreateFolderAsync(CreateFolderArg createFolderArg);
[Obsolete("This function is deprecated, please use CreateFolderAsync instead.")]
public Task<FolderMetadata> CreateFolderAsync(string path, bool autorename = false);
However, these messages do not make sense. Obviously, both messages should instead refer to the CreateFolderV2Async method.