Question Stopwatch on trigger enter

Hi, I'm new to Unity and I'm still learnig.
I made a little level where a ball has to reach the end before the timer reach the 0.
When the player reach the end a win screen appear and show you the score you have made and your time to complete the level.
What I want to know is: How can I stop the time in the winscreen after the player reached the end?

If they can be usefull down here there are the stopwatch script and the end trigger script:
Stopwatch:

Code (CSharp):

1.  
2. using System.Collections;
3. using System.Collections.Generic;
4. using TMPro;
5. using UnityEngine;
6.  
7. public class stopwatch : MonoBehaviour
8. {
9.     public float timeStart = 0;
10.     public TextMeshProUGUI textBox;
11.     private bool isGameStarted = false;
12.     private bool gameEnded = false;
13.  
14.     // Start is called before the first frame update
15.     void Start()
16.     {
17.         textBox.text = timeStart.ToString();
18.  
19.     }
20.  
21.     // Update is called once per frame
22.     void Update()
23.     {
24.  
25.        
26.             timeStart += Time.deltaTime;
27.             Debug.Log(timeStart);
28.        
29.         textBox.text = Mathf.Round(timeStart).ToString();
30.  
31.         if (timeStart < 0)
32.         {
33.             timeStart = 0;
34.             isGameStarted = false;
35.             gameEnded = true;
36.  
37.         }
38.  
39.         if (gameEnded == true)
40.         {
41.             FindObjectOfType<Gamemanager>().EndGame();
42.            
43.  
44.         }
45.     }
46. }

Endtrigger:

Code (CSharp):

1. using System.Collections;
2. using System.Collections.Generic;
3. using UnityEngine;
4.  
5. public class Endtrigger : MonoBehaviour
6. {
7.     public  Gamemanager Gamemanager;
8.     public GameObject Scermatadicountdown;
9.  
10.  
11.  
12.  
13.  
14.     private void OnTriggerEnter(Collider other)
15.     {
16.         Scermatadicountdown.GetComponent<countdown>().enabled = false;
17.         Gamemanager.Completelevel();
18.     }
19. }