If you want to create a Folder in C# on a Storage Account with Hierarchical namespace enabled. (in terraform is_hns_enabled = true).

You need to use the nuget : Azure.Storage.Files.DataLake

MSDN Documentation

_dataLakeServiceClient = new DataLakeServiceClient(new Uri($"{storageUri}"), new DefaultAzureCredential());

var fileSystemClient = _dataLakeServiceClient.GetFileSystemClient(_containerName);

DataLakeDirectoryClient directoryClient = await fileSystemClient.CreateDirectoryAsync(directoryName);