using System.Collections.Generic;

​

public interface IElement

{

}

​

public class AElement : IElement

{

    public void DoSomethingSpecial()

    { }

}

​

public class Container<TElement>

{

    public List<TElement> Elements { get; } = new();

}

​

​

​

public class Program

{

    public static Container<IElement> GetContainer()

    {

        var concreteContainer = new Container<AElement>();

        concreteContainer.Elements.ForEach(e => e.DoSomethingSpecial());

        return concreteContainer;

    }

    public static void Main()

    {

        var myContainer = GetContainer();

    }

}