using System;

using System.Globalization;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public class Item

    {

        public int Id;

        public string Date;

    }

    public static void Main()

    {

        string a = "01/31/2022";

        DateTime b = DateTime.Now;

        var articles = new List<Item>() { 

            new Item(){ Id = 1, Date = "01/01/2022"},

            new Item(){ Id = 2, Date = "12/03/2022"},

            new Item(){ Id = 3, Date = "08/10/2022"},

            new Item(){ Id = 4, Date = "10/10/2022"}

        };

        DateTime d;

        DateTime? c = DateTime.TryParseExact(a, "d/MM/yyyy", CultureInfo.InvariantCulture, DateTimeStyles.None, out d) ? d : (DateTime?) null;

        // a was not a valid string to convert, so c is null, just use a hard-coded date

        if(!c.HasValue)

        {

            c = new DateTime(2022, 10, 08); 

        }   

        IEnumerable<Item> mayoral = articles.Where(item => DateTime.ParseExact(item.Date.ToString(), "dd/MM/yyyy", null) > c);

        foreach(Item i in mayoral) Console.WriteLine(i.Date);

    }

}