How to freeze the position of an object when a canvas gets activated?

Hey jo. The best solution would be if you look for some Beginner C# and general Unity tutorials. Brackeys is a good Youtuber. You should check him out.

But i'll help you. The code is really self explaining :)

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

 public class IsCanvasEnabled : MonoBehaviour {

 public GameObject canvas;
 public Transform objectToFreeze;

 public float y;
 
 // Update is called once per frame
 void Update () {

     // If the Canvas Object in Scene is active ...
     if (canvas.activeInHierarchy)
     {
         // Set position of objectToFreeze
         objectToFreeze.position = new Vector3(objectToFreeze.position.x, y, objectToFreeze.position.z);

         // Use this instead if you want to freeze the object wich has this script
         transform.position = new Vector3(transform.position.x, y, transform.position.z);
     }
 }

}