AsClass.cs

class Program
    {
        private static readonly TestStruct _Account = new TestStruct();

        static void Main(string[] args)
        {
            Console.WriteLine(_Account.MyMoney);
            _Account.UpdateValue(100);
            Console.WriteLine(_Account.MyMoney);

            Console.WriteLine("Hello World!");
        }

        public class TestStruct
        {
            private int _money;
            public int MyMoney => _money;

            public void UpdateValue(int moneyAmount)
            {
                _money += moneyAmount;
            }
        }
    }

AsStruct.cs

class Program
    {
        private static readonly TestStruct _Account = new TestStruct();

        static void Main(string[] args)
        {
            Console.WriteLine(_Account.MyMoney);
            _Account.UpdateValue(100);
            Console.WriteLine(_Account.MyMoney);

            Console.WriteLine("Hello World!");
        }

        public struct TestStruct
        {
            private int _money;
            public int MyMoney => _money;

            public void UpdateValue(int moneyAmount)
            {
                _money += moneyAmount;
            }
        }
    }