How can I learn my List<CloudEvent> size as MB or KB?

Question

I am using CloudNative.CloudEvents nuget package from https://cloudevents.io/ for cloudevents issues.

I am getting the below error in my extension for binary serializer by using SerializeToUtf8Bytes() method.

Serialization and deserialization of 'System.Type' instances are not supported. Path: $.SpecVersion.IdAttribute.Type.ClrType.

  public static bool IsEventBatchReachedLimits<T>(this IEnumerable<T> list)
  {
     var options = new JsonSerializerOptions() { Encoder = JavaScriptEncoder.Create(UnicodeRanges.All) };

     var resultBytes = JsonSerializer.SerializeToUtf8Bytes(list, options);
     string[] sizes = { "B", "KB", "MB", "GB", "TB" };
        var len = Convert.ToDouble(resultBytes.Length);
        var order = 0;
        while (len >= 1024D && order < sizes.Length - 1)
        {
           order++;
           len /= 1024;
        }
        return (sizes[order] == "MB" && len >= 1) ? true : false;
     
  }

Can you tell me the reason why I can not serialize List to utf8 Bytes ?

Usage above extension: Type of cloudEvents list is List

:

Actually, my real question is How can I learn my list size as MB or KB?