How can i improve my loop? its too heavy to run

Hi there, im creating a scroll UI and im actually done, but however with my bad coding, this will work only if there is not more than 100 object, i tested for 5000 and it works! but it became very very heavy after i scroll for over 100, i know the problem is because im doing the whole loop every time, i had been trying to make it for every 50 but...... as my coding still is still newbie level, this is a big challenge for me Please anyone could help me this, Thanks

here is my loop coding

     void CheckBottom(){
         var p = GameObject.Find ("Content").transform;
         for (int i = 0; i < _objectHeight.Length; i++) {
             if (diffMaskCont > _lengthY [i]) {
                 if (GameObject.Find (i.ToString ()) == null) {
                     var spawnObject = GameObject.Instantiate (_instantiateObject [i]);
                     spawnObject.transform.SetParent (p);
                     spawnObject.name = i.ToString ();
                 }
             }
         }
     }
 
     void CheckTop(){
 
         var p = GameObject.Find("Content").transform;
         for (int i = _objectHeight.Length; i > 0; i--) {
             if (diffContMaskMax > _lengthY[i]) {
                 if (GameObject.Find (i.ToString ()) == null) {
                     var spawnObject = GameObject.Instantiate(_instantiateObject[i]);
                     spawnObject.transform.SetParent (p);
                     spawnObject.name = i.ToString();
                 }
             }
         }
     }

and this is my update coding

 void Update(){
 
         diffContMaskMax = Mathf.Round(_contentRect.offsetMax.y - _outMask.offsetMax.y);
         if (diffContMaskMax < 0) {
             diffContMaskMax = 0;
         }
         diffContMaskMin = Mathf.Round(_contentRect.offsetMin.y - _outMask.offsetMin.y);
         if (diffContMaskMin > 0) { 
             diffContMaskMin = 0;
         }
 
         diffMaskCont = Mathf.Round(_outMask.sizeDelta.y + _contentRect.offsetMax.y - _outMask.offsetMax.y);
 
 
         if (Mathf.Abs(_maskScrollRect.velocity.y) < forceZero) {
             _maskScrollRect.velocity = new Vector2( 0,0);
         }
 
         if (_maskScrollRect.velocity.y != 0) {
 
             if (_maskScrollRect.velocity.y > 0) {
                 CheckBottom ();
             } else {
                 CheckTop ();
             }
         }
     }