Using singleton or UnityEvent

Hi guys, In the game I am developing I rely on using singleton class GameManager to trigger functions to do stuffs such as update score, create die fx,etc.. Is this a good pratice or I should switch to use event? My Monster code

 public virtual  IEnumerator CheckDie()
     {       
         yield return new WaitUntil(() => current_hp <= 0);
         //OnDied?.Invoke();
         GameManager.Instance.UpdateScore(base_score);
         GameManager.Instance.CreateDieFx(transform.position);
         GameManager.Instance.sfx.PlayOneShot(GameManager.Instance.monster_die_sfx,0.3f);
         GameManager.Instance.camera_shake_fx.Shake();
         current_movespeed = base_movespeed;
         DropCoin();
         Lean.Pool.LeanPool.Despawn(this.gameObject);
     }

Example I use event

 public Vector3 origin_position;
 protected float t_lerp = 0.1f;
 public UnityEvent OnDie;

And I call it in the CheckDie

 public virtual  IEnumerator CheckDie()
     {       
         yield return new WaitUntil(() => current_hp <= 0);
         OnDie?.Invoke();
         GameManager.Instance.UpdateScore(base_score);
         GameManager.Instance.CreateDieFx(transform.position);
         GameManager.Instance.sfx.PlayOneShot(GameManager.Instance.monster_die_sfx,0.3f);
         GameManager.Instance.camera_shake_fx.Shake();
         current_movespeed = base_movespeed;
         DropCoin();
         Lean.Pool.LeanPool.Despawn(this.gameObject);
     }

I register it in a another spawner class

 monster.GetComponent<BaseMonster>().OnDie = TestEvent;
         monster.GetComponent<BaseMonster>().Run();
         wave_index += 1;

Then I setup it in Scene like this