How do I stop multiple spawns?

There's the solution with lists that comes to $$anonymous$$d and it should work as long as the colliders are on the same game object (if not, you can tell me later and with a slight modification it can work with that too)

 public class Spawn_Drone : MonoBehaviour
  {
  public Transform Drone;
  public Transform SpawnPoint;
  public Transform TeleportEffect;
  public List<GameObject> activators = new List<GameObject>();
 
  void OnTriggerEnter(Collider col)
  {
      if (col.gameObject.tag == "DroneActivator")
      {
        if(!activators.Contains(col.gameObject))
        {
          activators.Add(col.gameObject);
          Spawn();
          Debug.Log("Active 1: Spawn Drone script");
        }
      }
  }
 
 void OnTriggerExit(Collider col)
  {
      if (col.gameObject.tag == "DroneActivator")
      {
        if(activators.Contains(col.gameObject))
        {
          activators.Remove(col.gameObject);
          Debug.Log("collision ended, object removed from list");
        }
        else
        {
           Debug.Log("collision ended, but object was not in list");
         }
      }
  }
 
  void Spawn()
  {
      Instantiate(Drone, SpawnPoint.position, SpawnPoint.rotation);
      Instantiate(TeleportEffect, SpawnPoint.position, SpawnPoint.rotation); //addition
      Debug.Log("Drone Active: Spawn Drone script");
  }
 }

Even a bool could have worked here but i made it with a list so that you can even have multiple activator objects in case you ever need them....hope this helps!