How to generate GameObjects, then respawn them when they are stopped

I'm writing a system that instantiates clouds (prefabs that I created) in random locations. When they are spawned, they move to a spot via Vector2.MoveTowards. What I am trying to do, is check whether they stopped. And if they stopped, to create new ones.

My system:
Script 1 (Procedural Clouds (I know they are not procedurally created, but I started off naming the script this because that is what I want to achieve in the long run) ):

A public GameObject array where I store prefabs that I created, and these prefabs get instantiated in script.
One Vector3 (had to use Vector3 instead of 2 because I use Random.Range) which is one of the start positions (I have 6 start positions in total.)
At first I used InvokedRepeating in Start function to instantiate at random times, but I ditched that and decided to call my spawn-methods based on if the cloud has already been spawned or not. (I could try a coroutine with an IEnumerator, but I don't know if that will serve it's purpose here)

Script 2 (MoveClouds):

In start function I define three end positions which are Vector3.

This is where I start to struggle. I first tried to use .transform.position = Vector3.MoveTowards(). But my problem here was to check if the clouds had stopped. I tried hasChanged, but that did not work. So after a lot of Googling and trying to make it work, I decided to attach Rigidbody2D to the clouds, because I thought I could check if velocity.magnitude == 0, then they are stopped. I also applied both rb.velocity and rb.addforce, to that there is actual force to check if that force has stopped and a new one should be spawned. I do not want to use RB since they are not going to be related to any physics, they are simply just going to move from one random point to another specific point, then evaporate and when they are evaporated, then a new one spawns.

I know it's a long post, but I appreciate any help! I have been working in Unity for a little over 3 months, so I'm still pretty new to this.

My code: Script 1

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

public class ProceduralClouds : MonoBehaviour 
{
    public GameObject[] clouds;
    Vector3 startPos1, startPos2, startPos3, startPos4, startPos5, startPos6;
    [HideInInspector] public GameObject cloud1, cloud2, cloud3, cloud4, cloud5, cloud6;
    public bool cloud1Spawned, cloud2Spawned, cloud3Spawned, cloud4Spawned, cloud5Spawned, cloud6Spawned;

    private void Start()
    {
        
        /*InvokeRepeating(nameof(SpawnCloud1), 0, 20); 
        InvokeRepeating(nameof(SpawnCloud2), 1, 22); 
        InvokeRepeating(nameof(SpawnCloud3), 3, 25); 
        InvokeRepeating(nameof(SpawnCloud4), 0, 18); 
        InvokeRepeating(nameof(SpawnCloud5), 2, 20); 
        InvokeRepeating(nameof(SpawnCloud6), 5, 21); */
    }

    private void Update()
    {
        startPos1 = new Vector3(Random.Range(15, 25), Random.Range(0, 10), 0);
        startPos2 = new Vector3(Random.Range(15, 25), Random.Range(0, 10), 0);
        startPos3 = new Vector3(Random.Range(15, 25), Random.Range(0, 10), 0);
        startPos4 = new Vector3(Random.Range(15, 25), Random.Range(0, 10), 0);
        startPos5 = new Vector3(Random.Range(15, 25), Random.Range(0, 10), 0);
        startPos6 = new Vector3(Random.Range(15, 25), Random.Range(0, 10), 0);

        // test prints:

        print("Cloud 1 spawned: " + cloud1Spawned);

        SpawnCloud1();
        SpawnCloud2();
        SpawnCloud3();
        SpawnCloud4();
        SpawnCloud5();
        SpawnCloud6();
        
    }

    private void SpawnCloud1()
    {
        
        if (!cloud1Spawned)
        {
            cloud1 = Instantiate(clouds[Random.Range(0, clouds.Length)], startPos1, Quaternion.identity);
            cloud1Spawned = true;
        } 
    }

    private void SpawnCloud2()
    {
        
        if (!cloud2Spawned)
        {
            cloud2Spawned = true;
            cloud2 = Instantiate(clouds[Random.Range(0, clouds.Length)], startPos2, Quaternion.identity);
        }
    }

    private void SpawnCloud3()
    {
        
        if (!cloud3Spawned)
        {
            cloud3 = Instantiate(clouds[Random.Range(0, clouds.Length)], startPos3, Quaternion.identity);
            cloud3Spawned = true;
        }
    }

    private void SpawnCloud4()
    {
        
        if (!cloud4Spawned)
        {
            cloud4 = Instantiate(clouds[Random.Range(0, clouds.Length)], startPos4, Quaternion.identity);
            cloud4Spawned = true;
        }
    }

    private void SpawnCloud5()
    {
        
        if (!cloud5Spawned)
        {
            cloud5 = Instantiate(clouds[Random.Range(0, clouds.Length)], startPos5, Quaternion.identity);
            cloud5Spawned = true;
        }
    }

    private void SpawnCloud6()
    {
        
        if (!cloud6Spawned)
        {
            cloud6 = Instantiate(clouds[Random.Range(0, clouds.Length)], startPos6, Quaternion.identity);
            cloud6Spawned = true;
        }
    }
}

Script 2:

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

public class MoveClouds : MonoBehaviour
{
    public float step;
    private ProceduralClouds proCloudsScript;
    private GameObject cloud1, cloud2, cloud3, cloud4, cloud5, cloud6;
    private Vector3 endPosBottom, endPosMiddle, endPosTop;
    private void Start()
    {
        proCloudsScript = GameObject.Find("ScriptHandler").GetComponent<ProceduralClouds>();
        endPosBottom = new Vector3(-26, 8, 0);
        endPosMiddle = new Vector3(-26, 10, 0);
        endPosTop = new Vector3(-26, 12, 0);
    }

    private void Update()
    {
        cloud1 = proCloudsScript.cloud1;
        cloud2 = proCloudsScript.cloud2;
        cloud3 = proCloudsScript.cloud3;
        cloud4 = proCloudsScript.cloud4;
        cloud5 = proCloudsScript.cloud5;
        cloud6 = proCloudsScript.cloud6;

        float step = this.step * Time.deltaTime;
       /* cloud1.transform.position = Vector3.MoveTowards(cloud1.transform.position, endPosBottom, step);
        cloud2.transform.position = Vector3.MoveTowards(cloud2.transform.position, endPosTop, step);
        cloud3.transform.position = Vector3.MoveTowards(cloud3.transform.position, endPosMiddle, step);
        cloud4.transform.position = Vector3.MoveTowards(cloud4.transform.position, endPosTop, step);
        cloud5.transform.position = Vector3.MoveTowards(cloud5.transform.position, endPosBottom, step);
        cloud6.transform.position = Vector3.MoveTowards(cloud6.transform.position, endPosMiddle, step);*/

        cloud1.GetComponent<Rigidbody2D>().velocity = Vector2.MoveTowards(cloud1.transform.position, 
        endPosBottom, step);
        cloud2.GetComponent<Rigidbody2D>().velocity = Vector2.MoveTowards(cloud2.transform.position, 
        endPosMiddle, step);
        cloud3.GetComponent<Rigidbody2D>().velocity = Vector2.MoveTowards(cloud3.transform.position, 
        endPosTop, step);
        cloud4.GetComponent<Rigidbody2D>().velocity = Vector2.MoveTowards(cloud4.transform.position, 
        endPosTop, step);
        cloud5.GetComponent<Rigidbody2D>().velocity = Vector2.MoveTowards(cloud5.transform.position, 
        endPosBottom, step);
        cloud6.GetComponent<Rigidbody2D>().velocity = Vector2.MoveTowards(cloud6.transform.position, 
        endPosMiddle, step);



        if (cloud1.GetComponent<Rigidbody2D>().velocity.magnitude == 0 )
        {
            print("Cloud 1 is still");
            proCloudsScript.cloud1Spawned = false;
            print(cloud1.GetComponent<Rigidbody2D>().velocity.magnitude);
        }

        if (cloud2.GetComponent<Rigidbody2D>().velocity.magnitude == 0)
        {
            print("Cloud 2 is still");
            proCloudsScript.cloud2Spawned = false;
            print(cloud2.GetComponent<Rigidbody2D>().velocity.magnitude);
        }

        if (cloud3.GetComponent<Rigidbody2D>().velocity.magnitude == 0)
        {
            print("Cloud 3 is still");
            proCloudsScript.cloud3Spawned = false;
            print(cloud3.GetComponent<Rigidbody2D>().velocity.magnitude);
        }

        if (cloud4.GetComponent<Rigidbody2D>().velocity.magnitude == 0)
        {
            print("Cloud 4 is still");
            proCloudsScript.cloud4Spawned = false;
            print(cloud4.GetComponent<Rigidbody2D>().velocity.magnitude);
        }

        if (cloud5.GetComponent<Rigidbody2D>().velocity.magnitude == 0)
        {
            print("Cloud 5 is still");
            proCloudsScript.cloud5Spawned = false;
            print(cloud5.GetComponent<Rigidbody2D>().velocity.magnitude);
        }

        if (cloud6.GetComponent<Rigidbody2D>().velocity.magnitude == 0)
        {
            print("Cloud 6 is still");
            proCloudsScript.cloud6Spawned = false;
            print(cloud6.GetComponent<Rigidbody2D>().velocity.magnitude);
        }

    }
}

Solution

I see a lot of small issues in your code!

I would start with the usage of Vector3 .. if you actually want Vector2 then rather use that ;)
Implementing the same functionality over and over again just to have different numbers is really not good! Try to merger all this together into a single method. This is a) better for maintenance and b) for scalability!
You are passing a position generated by using
```
Vector2.MoveTowards(cloud1.transform.position, endPosBottom, step);
```
to a velocity -> makes no sense.
even though it was improved a lot in newer versions, using GetComponent over ad over again multiple times and every frame is extremely inefficient.
generating new random positions every frame and then throw them away most of the times since you don't spawn a cloud if it still moves is again very inefficient.

So I would do it like this

// Responsible for creating and initializing cloud instances
public class ProceduralClouds : MonoBehaviour 
{
    // As before here assign your prefabs
    // CloudMove is a dedicated script that will go onto your cloud prefabs
    // See next code snippet
    public CloudMove[] clouds;
    // How many clouds should be spawned?
    public int amountOfClouds = 6;

    // Configure your possible target position in the Inspector
    public Vector2[] targetPositions = { new Vector3(-26, 8, 0), new Vector3(-26, 10, 0), new Vector3(-26, 12, 0) };

    // This will keep track which target position chose next
    // (could make it random as well)
    private int currentTargetIndex;     

    private void Start()
    {
        // Spawn the first "wave" of clouds
        for(var i = 0; i < amountOfClouds; i++)
        {
            SpawnCloud();
        }
    }

    private void SpawnCloud()
    {
        // pick a random start position
        var startPos = new Vector2(Random.Range(15, 25), Random.Range(0, 10));
        // get the next target position
        var targetPos = targetPositions [currentTargetIndex];
        // Increase the index, wrap around if reaching end of array
        currentTargetIndex = (currentTargetIndex + 1) % targetPositions.Length;

        // instantiate the cloud
        var cloud = Instantiate(clouds[Random.Range(0, clouds.Length)], startPos, Quaternion.identity);
        // assign its target position
        // Could also pick a random speed here
        cloud.targetPosition = targetPos;
        // Assign a callback to an event we will implement
        // This is way better than poll check stuff in Update
        cloud.OnReachedTarget += SpawnCloud;
    }
}

And then another script that goes directly on your cloud prefabs:

// Responsible for moving one cloud instance
public class CloudMove : MonoBehaviour
{
    // Basically equals your step
    // But this way the clouds could even have individual speed values
    public float speed = 1;

    // Will be assigned by the spawner script
    public Vector2 targetPosition;
    // Whoever wants can be listening here
    public event Action OnReachedTarget;

    private void Update ()
    {
        // Move towards the target position with given speed 
        transform.position = Vector2.MoveTowards(transform.position, targetPosition, speed * Time.deltaTime);

        // Either use this check with a precision of 0.00001
        if((Vector2)transform.position == targetPosition)
        // Or alternatively if you need a more exact precision
        //if(Mathf.Approximately(Vector2.Distance(transform.position, targetPosition), 0))
        {
            // Invoke the event so whoever is listening is informed
            OnReachedTarget?.Invoke();

            // You might be interested in destroying this cloud once it reached its target
            //Destroy(gameObject):
        }
    }
}