private ExitEvent _OnStateExited;

void ExitEventExample(AnimancerComponent animancer, AnimationClip clip)
{
    var state = animancer.Play(clip);
    
    // One line initialization:
    (_OnStateExited ??= new(state, OnStateExited)).Enable();
    
    // Or two lines:
    _OnStateExited ??= new(state, OnStateExited);
    _OnStateExited.Enable();
}

private void OnStateExited()
{
    Debug.Log(_OnStateExited.State + " Exited");
}