Singleton.cs

public class Singleton
{
    private static readonly Lazy<Singleton> _lazy = new Lazy<Singleton>(
        () => new Singleton(), isThreadSafe: true);
        
    public static Singleton Instance
    {
        get
        {
            return Singleton._lazy.Value;
        }
    }
    
    private Singleton()
    {
    }
}

Modified by removing LazyThreadSafetyMode.ExecutionAndPublication in favor of a specified a named parameter (isThreadSafe) for human readability.