My player has to jump from one platform to another but I want to avoid double or multiple jumps as the player is jumping in air when clicked more than once. I don't know why my code isn't working. Can anyone help me out.?

public class PlayerController : MonoBehaviour
{
public float thrust;
public CameraController cameraController;
public TextMeshProUGUI scoreText;
public TextMeshProUGUI addScoreText;
[HideInInspector] public int score;

private int jumpcount;
private Rigidbody2D rb;

private void Start()
{
    rb = GetComponent<Rigidbody2D>();

    addScoreText.text = " ";
    score = 0;
    jumpcount = 0;
}

private void Update()
{
    if( Input.GetMouseButtonDown(0))
    {
        if(jumpcount==0)
        {
            rb.AddForce(new Vector3(0, thrust, 0), ForceMode2D.Impulse);
            jumpcount = jumpcount + 1;
        }
        else
        {
            
        }
        
    }
}

private void OnTriggerExit2D(Collider2D collision)
{
    if (collision.gameObject.CompareTag("Platform"))
    {
        collision.isTrigger = false;
        score += 5;
        Adding();
        Scoring();
        cameraController.Move();
        jumpcount = 0;
    }
}

private void OnCollisionExit2D(Collision2D collision)
{
    collision.collider.isTrigger = true;
   
}

private void Scoring()
{
    scoreText.text = "Score: " + score.ToString();
}

private void Adding()
{
    addScoreText.rectTransform.position = transform.position + new Vector3(800, 100, 0);
    addScoreText.text = " +5 ";
    Destroy(addScoreText, 1);
    
}

}

Just make an if Method, so when the player touches the ground or anything else, then he can jump. You have to let the colliders of both the player and the ground recognize the collision so use:

private void OnCollisionEnter2D (Collider2D collision)
    {
        if  (collision.gameObject.Tag.Equals("Ground, Wall, etc")
            { 
                //here you have to write you code for jumping, so in this case your AddForce Method
            }

If it is not working for you just delete the if method and do it like this. I dont know why it works but it works for me.

private void OnCollisionEnter2D (Collider2D collision)
    {
        //here you have to write you code for jumping, so in this case your AddForce Method
    }      

I hope you are able to do something with it.