<PackageReference Include="System.Reactive" Version="6.0.0" />

System.Reactive.EventPattern<TEventArgs>

public class EventPattern<TEventArgs> : EventPattern<object, TEventArgs>
Represents a .NET event invocation consisting of the weakly typed object that raised the event and the data that was generated by the event.
namespace System.Reactive { public class EventPattern<[System.Runtime.CompilerServices.Nullable(2)] TEventArgs> : EventPattern<object, TEventArgs> { public EventPattern(object sender, TEventArgs e); } }