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

System.Reactive.ExceptionHelper

static class ExceptionHelper
Utility methods to handle lock-free combining of Exceptions as well as hosting a terminal-exception indicator for lock-free termination support.
namespace System.Reactive { internal static class ExceptionHelper { public static Exception Terminated { get; } public static bool TrySetException(ref Exception field, Exception ex); } }