无法调用枚举扩展方法

我想为我的 Enum 以将值打印为字符串。我已经编写了以下静态扩展方法:

public enum Genre
{
    Action,
    Thriller,
    Comedy,
    Drama,
    Horror,
    SciFi,
}

public static class Extensions
{
    public static string StringBuilder(this Genre g)
    {
        switch (g)
        {
            case Genre.Action: return $"Action";
            case Genre.Thriller: return $"Thriller";
            case Genre.Comedy: return $"Comedy";
            case Genre.Drama: return $"Drama";
            case Genre.Horror: return $"Horror";
            case Genre.SciFi: return $"SciFi";
            default: return "";
        }
    }
}

扩展方法在另一个类中调用:

public class MovieItem
{
    public string? Title { get; }
    public int? RunningTimeMinutes { get; }
    public Enum Genre { get; }

    public MovieItem(string title, int runningTimeMinutes, Genre genre)
    {
        Title = title;
        RunningTimeMinutes = runningTimeMinutes;
        Genre = genre;
    }


    public override string ToString()
    {
        return $"Titel = {Title}, Varighed = {RunningTimeMinutes}, Genre = {Genre.StringBuilder(Genre)}";
    }
}

调用时出现问题 Genre.StringBuilder(Genre) 生产误差 CS1501 "No overload for method 'StringBuilder' takes 1 arguments" -但扩展方法显然需要论证。我错过什么了吗?