Call function after other objects have run their Start() function

Level Generator

  public void Update()
     {
          for(int i=0;i<30;i++)
          {
           Instantiate(RoomPrefab);
          }

Room Script

 public void Start()
 {
          for(int i=0;i<10;i++)
          { 
         GameObject temp=Instantiate(MiscGameobjects);
         MiscObjectPool .MiscObject_Positions.Add(temp);
          }
 }

SizeRandomizer // Similarly there is one for Sprite and one for Color

 public void Start()
 {
          transform.scale=new Vector3(Random.Ranger(1.0f,2.0f),Random.Ranger(1.0f,2.0f),Random.Ranger(1.0f,2.0f));              
 }

MIscObjectPool

 public class MiscObjectPool : MonoBehaviour {
     public class MiscObject_data
     {
         public Vector3 position;
         public Vector3 scale;
         public Color32 color32;
         public Sprite sprite;
 
         public MiscObject_data(Vector3 _pos ,Vector3 _scale ,Color32 _color32, Sprite _sprite)
         {
             this.position = _pos;
             this.scale = _scale;
             this.color32 = _color32;
             this.sprite = _sprite;
         }
 
     }
 
     public Dictionary<Vector3, MiscObject_data> MiscObject_Positions
 = new Dictionary<Vector3, MiscObject_data>();
     public static List<GameObject> MiscGOs = new List<GameObject>();
 
     **// When should i call this function in order to have the randomized MiscObj;**
     public void GetRandomized_MiscData()
     {
         foreach(GameObject miscGO in MiscGOs)
         {
             MiscObject_data data = new MiscObject_data(miscGO.transform.position,
                 miscGO.transform.localScale,
                 miscGO.GetComponent<SpriteRenderer>().color,
                 miscGO.GetComponent<SpriteRenderer>().sprite);
 
             MiscObject_Positions.Add(data.position, data);
         }
     }
 
 
 
     public void Update()
     {
         
         foreach(Vector3 _pos in MiscObject_Positions.Keys)
         {
             if (Vector3.Distance(_pos, transform.position)<10)
             {
                 // enable a pooled object in spesific _pos
                 // set its randomized size
                 // set its randomized Color;
             }
         }
     }
 
 }

I Instantiate MiscObjects like rocks on scene loading , after each rock is instantiated he changes between random rock sprites , color and size .

On camera the player can see around 25-30 rocks simultaneously .So i destroy all the generated rocks but keep the data after the randomizers and save them on a dictionary with their position as the key. So that I can pool 30 rocks instead of almost 200.

Thank you for your time

im not exactly sure if this will work, but maybe make a boolean and name it something like hasCalled and in the update function just do

 void Update() 
 {
     if (!hasCalled)
     {
         hasCalled = true;
         TheFunctionYouWannaCall();
     }
 }

so that way it will only be called once

if this is not what youre trying to do or if theres something wrong then let me know :)