Templates for C#

using System;
using System.Collections.Generic;
using System.IO;
namespace CarApp
{
    internal class Car
    {
        public int Id;
        public string Brand;
        public string Model;
        public int ManufactureYear;
        public string Color;
        public int SoldUnits;
        public int AverageSold;
        public int Id1 { get => Id; set => Id = value; }
        public string Brand1 { get => Brand; set => Brand = value; }
        public string Model1 { get => Model; set => Model = value; }
        public int ManufactureYear1 { get => ManufactureYear; set => ManufactureYear = value; }
        public string Color1 { get => Color; set => Color = value; }
        public int SoldUnits1 { get => SoldUnits; set => SoldUnits = value; }
        public int AverageSold1 { get => AverageSold; set => AverageSold = value; }
        public Car(int id, string brand, string model, int manufactureYear, string color, int soldUnits, int averageSold)
        {
            Id1 = id;
            Brand1 = brand;
            Model1 = model;
            ManufactureYear1 = manufactureYear;
            Color1 = color;
            SoldUnits1 = soldUnits;
            AverageSold1 = averageSold;
        }
        public Car(string line)
        {
            string[] data = line.Split(';');
            Id1 = int.Parse(data[0]);
            Brand1 = data[1];
            Model1 = data[2];
            ManufactureYear1 = int.Parse(data[3]);
            Color1 = data[4];
            SoldUnits1 = int.Parse(data[5]);
            AverageSold1 = int.Parse(data[5]);
        }
        public static List ReadFromFile(string fileName)
        {
            List carList = new List();
            string[] lines = File.ReadAllLines(fileName);
            for (int i = 1; i < lines.Length; i++)
            {
                Car c = new Car(lines[i]); 
                carList.Add(c);
            }
            return carList;
        }
    }
}

using System;
using System.Collections.Generic;
using System.Linq;
namespace CarApp
{
    internal class Program
    {
        static void Main(string[] args)
        {
            List cars = Car.ReadFromFile("autok.csv");
            Console.WriteLine($"Task 5: {cars.Count} cars found in the list");
            double totalSales = 0;
            foreach (Car car in cars)
            {
                totalSales += car.SoldUnits1;
            }
            double averageSales = totalSales / cars.Count;
            Console.WriteLine($"Task 6: The average number of sold cars is: {averageSales:F2} ");
            Console.WriteLine("Task 7: Cars manufactured in the last 5 years (2019 or later):");
            foreach (Car car in cars)
            {
                if (car.ManufactureYear1 >= 2019)
                {
                    Console.WriteLine($"\t- {car.Brand1} {car.Model1}: {car.ManufactureYear1}");
                }
            }
            Console.WriteLine($"Task 8: List of most successful brands based on sold units:");
            foreach (Car car in cars.OrderByDescending(c => c.SoldUnits))
            {
                Console.WriteLine($"\t-{car.Model1}: {car.SoldUnits1}");
            }
            // MAIN LOOP & MENU NAVIGATION
            bool isRunning = true;
            while (isRunning)
            {
                Console.WriteLine("\n--- Main Menu ---");
                Console.WriteLine("1. Search for a car model");
                Console.WriteLine("2. Exit");
                Console.Write("Choose an option: ");
                string menuChoice = Console.ReadLine();
                if (menuChoice == "1")
                {
                    Console.Write("Please enter a car model: ");
                    string input = Console.ReadLine();
                    bool isModelFound = false;
                    foreach (Car car in cars)
                    {
                        if (car.Model1 == input)
                        {
                            isModelFound = true;
                            break;
                        }
                    }
                    if (isModelFound)
                    {
                        Console.WriteLine("The requested model is found in the list!");
                    }
                    else
                    {
                        Console.WriteLine("The requested model is not found.");
                    }
                }
                else if (menuChoice == "2")
                {
                    isRunning = false;
                }
                else
                {
                    Console.WriteLine("Invalid option.");
                }
            }
        }
    }
}

I read that as a TUI (Text-based User Interface) Application. There is a subtle difference between CLI and TUI. Anyway, in either case:

Apart from trying and failing as much as you can, I'd also recommend to at some time in, have a look into Spectre Console.

Why those properties? It doesn't make sense.