Problem with targeting system

I have a targeting system and it will target an enemy and than ill fight them and kill them and than once i kill them in the enemy ai script i have this

For my Player script i am using system.collections.generic

 if(Health <= maxHealth) {
     Destroy(transform.gameObject);
 }

Once the object gets destroyed i get this error

 MissingReferenceException: The object of type 'Transform' has been destroyed but you are still trying to access it.
 Your script should either check if it is null or you should not destroy the object.
 UnityEngine.Transform.get_position () (at C:/BuildAgent/work/842f9557127e852/Runtime/ExportGenerated/Editor/UnityEngineTransform.cs:19)
 PlayerController.<SortTargets>m__0 (UnityEngine.Transform t1, UnityEngine.Transform t2) (at Assets/My Assets/Scripts/Player/PlayerController.cs:65)
 System.Array.qsort[Transform] (UnityEngine.Transform[] array, Int32 low0, Int32 high0, System.Comparison`1 comparison)
 System.Array.Sort[Transform] (UnityEngine.Transform[] array, Int32 length, System.Comparison`1 comparison)

After getting this error i am no longer able to target. I know what the error means but i dont know how to fix.

Heres the code that the errors is in

 public void Targeting() {
         GameObject[] go = GameObject.FindGameObjectsWithTag("Enemy");
         
         foreach(GameObject enemy in go){
             AddTarget(enemy.transform);    
         }
     }
     public void AddTarget(Transform enemy){
         targets.Add(enemy);
     }
     private void SortTargets() {
         targets.Sort(delegate(Transform t1, Transform t2) { 
             return Vector3.Distance(t1.position, transform.position).CompareTo(Vector3.Distance(t2.position, transform.position));
                     });
     }
     public void ActualTarget() {
         if(Target == null) {
             SortTargets();
             Target = targets[0];
         }
         else
         {
             int index = targets.IndexOf(Target);
             
             if(index < targets.Count - 1) {
                 index++;
             }
             else
             {
                 index = 0;    
             }
             DeselectTarget();
             Target = targets[index];
             
         }
         SelectTarget();
     }
     
     private void SelectTarget() {
         Target.renderer.material.color = Color.red;
         
         SelectedEnemy = Target.gameObject;
     }
     
     private void DeselectTarget() {
         Target.renderer.material.color = Color.yellow;    
         Target = null;
     }
     
     void Update() {
         
         if(SelectedEnemy == null) {
             ActualTarget();
         }
         
         
         if(Input.GetKeyDown(KeyCode.Tab)){
             ActualTarget();    
         }
         
     }

I obviously have the variables for this or it wouldnt work in the first place.