spawn things (once!)

SpawnObject.cs

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

public class SpawnObject : MonoBehaviour
{

    public List<Transform> possiblePositions = new List<Transform>();
    public List<GameObject> allThings = new List<GameObject>();

    void Start()
    {

        // do something as long as objects in the array exist
        for (int i = possiblePositions.Count; i > 0; i--)
        {
            
            int rndObject = Random.Range(0, allThings.Count);// generate a number from 0 to possible objects in the list (that changes)

            Instantiate(allThings[rndObject], possiblePositions[0].position, Quaternion.identity);// spawn object at the 1st spawn point 
            possiblePositions.RemoveAt(0); // remove spawn position that has been used!!
            allThings.RemoveAt(rndObject); // remove the spawned object that has been used!!
        }
    }

}