Script not working in build version

So in my game, I have this object that is supposed to jump continuously. The game works just fine when running it with unity remote 5. But when I try to build and run it, the object doesn't jump. The console outputs nullreferenceexception. After some fiddling, I found out that it can not find any object with tag "Ground". This is weird because there is an object with this tag and the game recognizes it when running it through unity.

None of my objects have the EditorOnly tag, and I have also tried setting the ground object to public to see if it works. And it still doesn't. Can anyone see what the problem is?

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 public class Jump : MonoBehaviour
 {
     private float jumpForce = 500f;
     private Rigidbody2D rb;
     private bool isGrounded;
     private float maxDistance = 0.75f;
     private GameObject ground;
 
     void Start()
     {
         isGrounded = false;
         rb = GetComponent<Rigidbody2D>();
         ground = GameObject.FindGameObjectWithTag("Ground");
     }
 
     void Update()
     {
         if (Vector3.Distance(ground.transform.position, GameObject.FindGameObjectWithTag("Platform").transform.position) < maxDistance)
         {
             if (isGrounded == true)
             {
                 rb.AddForce(transform.up * jumpForce);
                 isGrounded = false;
             }
             ground.SetActive(true);
         }
         else
         {
             ground.SetActive(false);
         }
     }
 
     void OnCollisionEnter2D(Collision2D coll)
     {
         if (coll.gameObject.tag == "Ground")
         {
             isGrounded = true;
         }
         else
         {
             isGrounded = false;
         }
     }
 }