Unable to get queue length / message count from Azure

The CloudQueue method has been deprecated (along with the v11 SDK).

The following snippet is the current replacement (from the Azure Docs)

//-----------------------------------------------------
// Get the approximate number of messages in the queue
//-----------------------------------------------------
public void GetQueueLength(string queueName)
{
    // Get the connection string from app settings
    string connectionString = ConfigurationManager.AppSettings["StorageConnectionString"];

    // Instantiate a QueueClient which will be used to manipulate the queue
    QueueClient queueClient = new QueueClient(connectionString, queueName);

    if (queueClient.Exists())
    {
        QueueProperties properties = queueClient.GetProperties();

        // Retrieve the cached approximate message count.
        int cachedMessagesCount = properties.ApproximateMessagesCount;

        // Display number of messages.
        Console.WriteLine($"Number of messages in queue: {cachedMessagesCount}");
    }
}

https://docs.microsoft.com/en-us/azure/storage/queues/storage-dotnet-how-to-use-queues?tabs=dotnet#get-the-queue-length

RetrieveApproximateMessageCount() has been deprecated

if you want to use ApproximateMessageCount to get result try this

CloudQueue q = queueClient.GetQueueReference(QUEUE_NAME);
q.FetchAttributes();
qCnt = q.ApproximateMessageCount;