How to create a save using PlayerPrefs?

Question

C++ / C#

When creating, the developer who explains the principle of saving refers to the List:

public List<Item> shopItems = new List<Item>();
private Save sv = new Save();
 sv = JsonUtility.FromJson<Save>(PlayerPrefs.GetString("SV"));
            score = sv.score;
            for (int i = 0; i < shopItems.Count; i++)
            {
                shopItems[i].levelOfItem = sv.levelOfItem[i];
                shopItems[i].bonusCounter = sv.bonusCounter[i];
                if (shopItems[i].needCostMultiplier) shopItems[i].cost *= (int)Mathf.Pow(shopItems[i].costMultiplier, shopItems[i].levelOfItem);
                if (shopItems[i].levelOfItem != 0) scoreIncrease += (int)Mathf.Pow(shopItems[i].bonusIncrease, shopItems[i].levelOfItem);
public class Save
{
    public int score;
    public int[] levelOfItem;
    public int[] bonusCounter;
}

In my case, I need to save the number of points and "Workforce", which gives a passive accumulation of points. My code :

public int score;
 public int bonus = 1;
 public int WorkersCount;

  public Save SaveGame = new Save();
 private void OnApplicationQuit()
   {    
      SaveGame.score = score;
      SaveGame.WorkersCount = new int [WorkersCount.Count];
      for (int i = 0; i < WorkersCount.Count; i++)
      {
         SaveGame.WorkersCount[i] = WorkersCount[i].WorkersCount;
      }
      PlayerPrefs.SetString("GameSave", JsonUtility.ToJson(SaveGame));
   }

   [Serializable]
   public class Save
   {
      public int score;
      public int [] WorkersCount;
   }

In my case, the engine swears at me:
1. Cannot apply indexing with [] to an expression of type 'int
2.'int' does not contain a definition for 'Count' and no accessible extension method 'Count' accepting a first argument of type 'int' could be found