sample.cs

using System;
using System.Collections.Generic;
using System.Linq;

namespace ConsoleApp9
{
    public class Tenant
    {
        public string Key { get; set; }

        public string Description { get; set; }
    }

    public class User
    {
        public int Id { get; set; }

        public string Name { get; set; }

        public IList<UserRequest> Requests { get; } = new List<UserRequest>();

        public string Tenant { get; set; }
    }

    public class Request
    {
        public int Id { get; set; }

        public string Name { get; set; }

        public DateTime TimeStamp { get; set; }

        public string Category { get; set; }

        public IList<UserRequest> Users { get; } = new List<UserRequest>();
    }

    public class UserRequest
    {
        public User User { get; set; }

        public int UserId { get; set; }

        public Request Request { get; set; }

        public int RequestId { get; set; }
    }

    public class UserView
    {
        public int Id { get; set; }

        public string Name { get; set; }

        public int LastRequestId { get; set; }

        public string LastRequestName { get; set; }

        public DateTime LastRequestTimeStamp { get; set; }
    }

    public class TenantView
    {
        public string Key { get; set; }

        public string Description { get; set; }

        public int UserId { get; set; }

        public string UserName { get; set; }
    }

    public class RequestsView
    {
        public int UserId { get; set; }

        public string UserName { get; set; }

        public int Year { get; set; }

        public int Month { get; set; }

        public int Count { get; set; }
    }

    public class RequestView
    {
        public int UserId { get; set; }

        public string UserName { get; set; }

        public int RequestId { get; set; }

        public string RequestName { get; set; }
    }

    public static class Examples
    {
        public static IEnumerable<UserView> LetStatement(IEnumerable<User> users)
        {
            return from u in users
                   let ur = u.Requests.OrderBy(r => r.Request.TimeStamp).Last()
                   let r = ur.Request
                   select new UserView
                   {
                       [||]
                   };
        }

    
    }
}