If you need to print the details of the Product, you should override the ToString() method. You can do this by using the below implementation of the Product class

public abstract class Product {
    protected string Name;
    protected int Quantity;

    public override string ToString() {
        return $"Name = {Name}, Quantity = {Quantity}";
    }
}

While I am at it, you might as well make some other minor improvements to your code. See the full code below

namespace ShoppingList {
    class ShoppingList {
        static void Main(string[] args) {
            Grocery myGrocery = new Grocery("Bread", 1);
            FreshProduce myFreshProduce = new FreshProduce("Orange", 1);

            List<Product> myShoppingList = new List<Product>();
            myShoppingList.Add(myGrocery);
            myShoppingList.Add(myFreshProduce);

            PrintValues(myShoppingList, "\t");
        }

        // instead of IEnumerable, you should use IEnumerable<Product> for better type checking
        public static void PrintValues(IEnumerable<Product> myList, string mySeparator) {
            // string.Join does exactly what you are trying to do using a loop
            Console.WriteLine(string.Join(mySeparator, myList));
        }


        public abstract class Product {
            protected string Name;
            protected int Quantity;

            public override string ToString() {
                return $"Name = {Name}, Quantity = {Quantity}";
            }
        }

        public class Grocery : Product {
            public Grocery(string groceryName, int groceryQuantity) {
                Name = groceryName;
                Quantity = groceryQuantity;
            }
        }
        public class FreshProduce : Product {
            public FreshProduce(string freshProduceName, int freshProduceQuantity) {
                Name = freshProduceName;
                Quantity = freshProduceQuantity;
            }

        }

    }
}