(UI Toolkit) "Destroy may not be called from edit mode" on game start

The game doesn't crash at all, I'm just getting a red error message whenever I stop the game and press the IDE's play button again.

The error says:

 Destroy may not be called from edit mode! Use DestroyImmediate instead.
 Destroying an object in edit mode destroys it permanently.
 UnityEngine.UIElements.PanelSettings:OnDisable ()

The scene contains UIDocument with a C# script for controlling the UI.

 public class MainMenuController : MonoBehaviour
 {
     public Button multiplayerButton, trainingButton, accountButton, shopButton;
 
     void Start()
     {
         var root = GetComponent<UIDocument>().rootVisualElement;
         multiplayerButton = root.Q<Button>("multiplayer-button");
         trainingButton = root.Q<Button>("training-button");
         accountButton = root.Q<Button>("account-button");
         shopButton = root.Q<Button>("shop-button");
 
         multiplayerButton.clicked += MultiplayerPressed;
         trainingButton.clicked += TrainingPressed;
         accountButton.clicked += TrainingPressed;
         shopButton.clicked += ShopPressed;
     }
 
     void MultiplayerPressed() {
         Debug.Log("M");
     }
 
     void TrainingPressed() {
         Debug.Log("T");
     }
 
     void AccountPressed() {
         Debug.Log("A");
     }
 
     void ShopPressed() {
         Debug.Log("S");
     }
 }