<PackageReference Include="System.Reactive" Version="6.1.0" />

System.Reactive.IEventPattern<TSender, TEventArgs>

public interface IEventPattern<TSender, TEventArgs>
Represents a .NET event invocation consisting of the strongly typed object that raised the event and the data that was generated by the event.
namespace System.Reactive { public interface IEventPattern<out TSender, out TEventArgs> { TSender Sender { get; } TEventArgs EventArgs { get; } } }