How can I call a class that extends interface?

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C#

I have a interface class:

public interface IStatFunction : IComparable<IStatFunction>
    {
        
    }

and normal class extends IStatFunction interface:

public class StatFunction : IStatFunction
    {
        
    }

Now my code will use both of above class and interface:

public void addEffect(IStatOwner statOwner, List<IStatFunction> functions)
        {
            
        }

other code call this addEffect function:

List<StatFunction> allModifiers = null;
            cgs.addEffect(item, allModifiers);

Now i get error: Cannot convert List<statfunction> to List<istatfunction>

so how can i fix this error?

What I have tried:

Im trying to use ConvertAll, its can remove error but i dont know its work or not:

cgs.addEffect(item, allModifiers.ConvertAll(o => (IStatFunction)o));