Will delete objects in Editor but not in Build?

So i have a problem. In my Menu Screen i have an arsenal tab. There is a table where the gun hovers above it and when i hit the left arrow or right arrow it switches trough the weapons showing their prefab in the screen.

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 public class ArsenalManager : MonoBehaviour {
 
     public GameObject[] guns;
     public Transform spawnPosition;
     public int gunIndex;
     Transform instantiatedGun;
     int[] levelNeeded = new int[5];
     int currentLevel;
 
     
 
     private void Start()
     {
         for(int i = 0; i< guns.Length; i++)
         {
             levelNeeded[i] = i * 5;
         }
     }
 
     public void OnCall()
     {
         RenderGun();
     } 
 
     void RenderGun()
     {
         //GameObject toDelete = GameObject.FindGameObjectWithTag("ArsenalWeapon");
         DestroyImmediate(GameObject.FindGameObjectWithTag("ArsenalWeapon"));
         Transform clone = Instantiate(guns[gunIndex].transform,spawnPosition.position, Quaternion.Euler((gunIndex==0)?180:0 ,-90,0));
     }
 
     public void LeftButton()
     {
         if (gunIndex > 0)
         {
             gunIndex--;
             RenderGun();
         }
         else
         {
             return;
         }
     }
 
     public void RightButton()
     {
         if (gunIndex < 4)
         {
             gunIndex++;
             RenderGun();
         }
         else
         {
             return;
         }
     }
 
     public int[] OnAcceptClick()
     {
         int[] trueAndLevel = new int[2];
         currentLevel = PlayerPrefs.GetInt("level", 0);
         if(currentLevel >= levelNeeded[gunIndex])
         {
             PlayerPrefs.SetInt("currentgun", gunIndex);
             trueAndLevel[0] = 1;
             trueAndLevel[1] = 0;
             return trueAndLevel;
         }
         trueAndLevel[0] = 0;
         trueAndLevel[1] = levelNeeded[gunIndex];
         return trueAndLevel;
     }
 
 }

Now i assigned the Tag to the weapons and in the editor when i run the game it works perfectly fine. when i hit left or right the old gun gets deleted and the new model is showed.

As soon as i built it it doesnt work anymore.

I even downloaded the EditorTag Finder script and modivied it to possibly find those tags but it tells me there are no editor tags. what is the problem?

 // xeophin.net/code // // (c) 2010 Kaspar Manz // code@xeophin.net // // All rights reserved. //
 using System;
 using UnityEngine;
 using UnityEngine.SceneManagement;
 
 [AddComponentMenu("Helper Scripts/List Objects By Tag")]
 
 ///
 
 /// This is a simple little script that lists all objects with a /// certain tag, in order to find wrongly tagged objects. ///
 public class TagFinder : MonoBehaviour
 {
     /// <summary>
     /// A list of tags to look for.
     /// </summary>
     public string[] tagsToFind = { "EditorOnly" };
     string sceneName;
 
     /// <summary>
     /// At the start of the game, this script lists all objects
     /// with the defined tags.
     /// </summary>
     void Start()
     {
         findTags();
         sceneName = SceneManager.GetActiveScene().name;
 
     }
 
     void findTags()
     {
         foreach (string tag in tagsToFind)
         {
             print("Objects tagged with '" + tag + "':");
 
             try
             {
                 GameObject[] objects = GameObject.FindGameObjectsWithTag(tag);
                 if (objects.Length != 0)
                 {
                     foreach (GameObject item in objects)
                     {
                         print("  " + item.name + " on layer " + item.layer);
                     }
                 }
                 else
                 {
                     print("  There are no objects with the tag '" + tag + "'.");
 
                 }
             }
             catch (UnityException ex)
             {
                 print("  The tag '" + tag + "' has not been found. Exception Message: " + ex.Message);
             }
 
         }
     }
 
     private void Update()
     {
         if(SceneManager.GetActiveScene().name != sceneName)
         {
             sceneName = SceneManager.GetActiveScene().name;
             findTags();
         }
 
         if (Input.GetKeyDown(KeyCode.T))
         {
             findTags();
         }
     }
 }