Learn how to save the runtime instantiated game objects.

ObjectSpawner.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

using SaveGamePro;

public class ObjectSpawner : MonoBehaviour {

  public GameObject prefab;
  public Transform spawnPoint;
  public List<Transform> spawnedGameObjects;
  
  void Awake () {
    Load ();
  }
  
  void OnApplicationQuit () {
    Save ();
  }
  
  public void Spawn () {
    GameObject go = Instantiate<GameObject> (prefab, spawnPoint.transform.position, Quaternion.identity);
    spawnedGameObjects.Add (go.transform);
  }
  
  public void Save () {
    SaveGame.Save<Transform> (spawnedGameObjects, "spawnedGameObjects");
  }
  
  public void Load () {
    if (SaveGame.Exists ("spawnedGameObjects")) {
      spawnedGameObjects = SaveGame.LoadList<Transform> ("spawnedGameObjects");
    } else {
      spawnedGameObjects = new List<Transform> ();
    }
    foreach (Transform tr in spawnedGameObjects) {
      Instantiate<GameObject> (prefab, tr.position, tr.rotation);
    }
  }

}