Which of the 23 classic patterns described in the book 'Design Patterns: Elements of Reusable Object-Oriented Software' have you applied in your projects?

In projects, I often use the following patterns from the classic 23:

• Singleton — to ensure a single instance of a class, for example, for a logger.
• Factory Method — to create objects without binding to specific classes.
• Observer — to implement event subscription, for example, in UI.
• Strategy — to choose an algorithm at runtime.
• Decorator — to dynamically extend the functionality of objects.

Example of using the Singleton pattern in C#:

public sealed class Logger
{
    private static readonly Logger instance = new Logger();
    private Logger() { }
    public static Logger Instance => instance;
    public void Log(string message) {
        Console.WriteLine(message);
    }
}