MoveToPlayer.cs

using UnityEngine;
public class MoveToPlayer : MonoBehaviour
{
   public Transform player;
   public float speed;
   public float maxDistance;
  
   void Update()
   {
       if (Vector3.Distance(player.position, transform.position) < maxDistance)
       {
           float step = speed * Time.deltaTime;
           transform.position = Vector3.MoveTowards(transform.position, player.position, step);
       }
   }
}

Bad example of how to structure unity behaviours