Events from an interface

events.cs

// interface
public interface IService 
{
  // other stuff, but nothing related to events
}

// inheriting class
public class Service : IService
{
  public static event EventHandler<MyEventArgs> SomethingHappened;
  
  public void SomeMethod() {
    SomethingHappened?.Invoke(this, new MyEventArgs());
  }  
}

// app start
public class RegisterEvents : ApplicationEventHandler
{
  protected override void ApplicationStarted(UmbracoApplicationBase umbracoApplication, ApplicationContext applicationContext)
  {
    Service.SomethingHappened += Service_SomethingHappened;     
  }
  
  private void Service_SomethingHappened(object sender, MyEventArgs e)
  {   
    // do stufff
  }
}