Why can't gameobject in the hierarchy find it without problems?

Question

I want to find the GameObject that is in the hierarchy correctly in the hierarchy. But this does not happen correctly, so I want 'if' to work when the gameobject I have tagged is active, but 'if' works even though there is no other gameobject tag, which is why this problem is caused.

Note: My level of English is not good, I try to explain the problem to you as much as I can, please tell me if there is anything you do not understand, I will try to explain it in detail as much as I can. Thank you for your understanding.

1. Image tagged gameobject: enter image description here
2. The point where the problem occurred: enter image description here
3. Gameobject tag name: enter image description here
4. Cubes Gameobject: enter image description here

    void Update()
    {
        if (cubes.instance.objPool.Count == 1) //It works when the number of gameobject in the list is 1 when I do a random deletion.
        {
            RewardSystem();
        }
    }
 
 
public void RewardSystem()
    {
        GameObject FoundCube = GameObject.FindGameObjectWithTag(cube_Tag_Number);
 
 
        if (FoundCube == null)
        {
            SoundManager.instance.GameOverMenuSound();
            game_Over_Menu.SetActive(true);
 
            next_Level_Menu.SetActive(false);
            confetti.Stop();
            clickButton.gameObject.SetActive(false);
            missionButton.gameObject.SetActive(false);
            enabled = false;
        }
        if (FoundCube != null)// problematic if
        {
            if (FoundCube.activeInHierarchy == true) // problematic if
            {
                SoundManager.instance.NextLevelMenuSound();
                next_Level_Menu.SetActive(true);
                confetti.Play();
 
                game_Over_Menu.SetActive(false);
                clickButton.gameObject.SetActive(false);
                missionButton.gameObject.SetActive(false);
                enabled = false;
            }
        }
    }
 
 
public class cubes : MonoBehaviour
{
    public static cubes instance;
 
    public int randomRangeNumber1, randomRangeNumber2;
 
    public List<GameObject> objPool = new List<GameObject>();
 
    private void Awake()
    {
        if (instance == null)
        {
            instance = this;
        }
        else if (instance != null)
        {
            Destroy(gameObject);
        }
 
    }
 
    public void ButtonOnDown()
    {
        SoundManager.instance.LuckButtonSound();
 
         for (int i = 0; i < 1; i++)
         {
            int index = Random.Range(randomRangeNumber1, randomRangeNumber2);
            GameObject.Destroy(objPool[index]);
            objPool.RemoveAt(index);
 
            randomRangeNumber2 = objPool.Count;
         }
    }
}