Еще один метод сериализации и десериализации .xml

SerializeOrDeserialize.cs

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Xml.Serialization;

namespace CONSOLE_TEST_SOLUTION
{
    class Program
    {
        static void Main(string[] args)
        {
            string filePath = ("" + Directory.GetCurrentDirectory() + "\\server-list-1.xml");

            // Вызов десериализации
            var desServers = DeserializeServers(filePath);

            // Получаем конкретный сервер
            var anyServer = desServers.FirstOrDefault(s => s.Name == "Server-3");

            // Получаем по конкретному адресу девайс
            foreach(var ser in desServers)
            {
                bool isExist = false;

                if(ser.Name == "Server-3")
                {
                    foreach(var dev in ser.Devices)
                    {
                        if (dev.Address == 1)
                        {
                            Console.WriteLine($"address: {dev.Address}; mode: {dev.Mode}; active: {dev.IsActive}");
                            isExist = true;
                            break;
                        }
                    }
                }
                if (isExist)
                    break;
            }

            // Выводим весь список
            foreach(var ser in desServers)
            {
                Console.WriteLine(ser.Name);
                foreach(var dev in ser.Devices)
                {
                    Console.WriteLine($"address: {dev.Address}; mode: {dev.Mode}; active: {dev.IsActive}");
                }
            }

            Console.ReadKey();
        }

        // Метод Сериализации
        public static void SerializeServers(List<Server> servers, string filePath)
        {
            XmlSerializer formatter = new XmlSerializer(typeof(List<Server>));
            using (FileStream fileStream = new FileStream(filePath, FileMode.OpenOrCreate))
            {
                formatter.Serialize(fileStream, servers);
            }
        }
        // Метод Десериализации
        public static List<Server> DeserializeServers(string filePath)
        {
            List<Server> servers = new List<Server>();

            XmlSerializer formatter = new XmlSerializer(typeof(List<Server>));

            using (FileStream fileStream = new FileStream(filePath, FileMode.OpenOrCreate))
            {
                servers = (List<Server>)formatter.Deserialize(fileStream);
            }

            return servers;
        }
    }

    // Структура для Девайсов
    [Serializable]
    public class Device
    {
        public byte Address { get; set; }
        public byte Mode { get; set; }
        public bool IsActive { get; set; }

        public Device() { }

        public Device(byte address, byte mode, bool isActive)
        {
            Address = address;
            Mode = mode;
            IsActive = isActive;
        }
    }

    // Структура для Серверов
    [Serializable]
    public class Server
    {
        public string Name { get; set; }
        public List<Device> Devices { get; set; }
        public Server() { }
        public Server(string name)
        {
            Name = name;
        }
    }
}

server-list-1.xml

<?xml version="1.0"?>
<ArrayOfServer xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:xds="http://www.w3.org/2001/XMLSchema">
	<Server>
		<Name>Server-3</Name>
		<Devices>
			<Device>
				<Address>1</Address>	
				<Mode>1</Mode>
				<IsActive>true</IsActive>
			</Device>
			<Device>
				<Address>2</Address>
				<Mode>2</Mode>
				<IsActive>true</IsActive>
			</Device>
			<Device>
				<Address>3</Address>
				<Mode>1</Mode>
				<IsActive>true</IsActive>
			</Device>
			<Device>
				<Address>4</Address>
				<Mode>2</Mode>
				<IsActive>true</IsActive>
			</Device>
			<Device>
				<Address>5</Address>
				<Mode>1</Mode>
				<IsActive>true</IsActive>
			</Device>
			<Device>
				<Address>6</Address>
				<Mode>2</Mode>
				<IsActive>true</IsActive>
			</Device>
			<Device>
				<Address>7</Address>
				<Mode>1</Mode>
				<IsActive>true</IsActive>
			</Device>
			<Device>
				<Address>8</Address>
				<Mode>2</Mode>
				<IsActive>true</IsActive>
			</Device>
			<Device>
				<Address>9</Address>
				<Mode>1</Mode>
				<IsActive>true</IsActive>
			</Device>
			<Device>
				<Address>10</Address>
				<Mode>1</Mode>
				<IsActive>true</IsActive>
			</Device>
			<Device>
				<Address>11</Address>
				<Mode>1</Mode>
				<IsActive>true</IsActive>
			</Device>
			<Device>
				<Address>12</Address>
				<Mode>1</Mode>
				<IsActive>true</IsActive>
			</Device>
			<Device>
				<Address>13</Address>
				<Mode>1</Mode>
				<IsActive>true</IsActive>
			</Device>
			<Device>
				<Address>14</Address>
				<Mode>1</Mode>
				<IsActive>true</IsActive>
			</Device>
			<Device>
				<Address>15</Address>
				<Mode>1</Mode>
				<IsActive>true</IsActive>
			</Device>
			<Device>
				<Address>16</Address>
				<Mode>1</Mode>
				<IsActive>true</IsActive>
			</Device>
		</Devices>
	</Server>

</ArrayOfServer>