Have you tried to get the section with XDocument? You can try the below code to get the desired section:
XDocument doccs = XDocument.Load("config_file_path");
XElement sectionsd = doccs.Root.Elements("section").Where(a => a.Attribute("name").Value == "serial1").FirstOrDefault();
You can parse the XElement into your target object through XmlSerializer. However, there are some issues in the config XML structure that need to be correct as well, fixed the typo in the "Parity" attribute in the section.