using System;

using System.Collections.Generic;

using System.Linq;

​

public class Program

{

    public static void Main()

    {

        var listA = new List<MyObject>{new()

        {OperationId = 123, Mode = "In-Transit", Location = "ATL", }, new()

        {OperationId = 234, Mode = "Delivered", Location = "PHX", }, new()

        {OperationId = 345, Mode = "Delivered", Location = "COL", }};

        var listB = new List<MyObject>{new()

        {OperationId = 123, Mode = "In-Transit", Location = "ATL", }};

        var usingExcept = listA.Except(listB);

        Console.WriteLine(usingExcept.Count());

        listA.RemoveAll(x => listB.Exists(y => y.OperationId == x.OperationId));

        Console.WriteLine(usingExcept.Count());

    }

}

​

public class MyObject

{

    public int OperationId { get; set; }

    public string Mode { get; set; }

    public string Location { get; set; }

}