Why does object spawning work incorrectly?

Question

Unity

Hello everyone, I'm trying to spawn objects when the character is on the ground. I'm trying to implement this through "Coroutine", but the objects spawn very quickly, a few per second, I think. The time limiter is worth it. What to do?

public GameObject enemy;
    public PlayerMovement PlayerMovementScript;
    // Start is called before the first frame update
    void Start()
    {
    }

    // Update is called once per frame
    void Update()
    {
         StartCoroutine(da());
    }

    IEnumerator da()
    {
        while (PlayerMovementScript.isGrounded == true)
        {
            Instantiate(enemy, new Vector3(Random.Range(-30, 30), 1f, Random.Range(-30, 30)), Quaternion.identity);
            yield return new WaitForSeconds(3f);
        }
    }

Answer 1

And why are you starting a coroutine in an update? You have her START run every frame.
The coroutine needs to be started ONCE - it will wrap itself in an update