Не меняется значение переменной

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
 
public class MainGame : MonoBehaviour
{
    internal int gameMod = -1;
 
    private void OnGUI() 
    {
        Debug.Log("D02 gameMod OnGUI = " + gameMod);
        float centrScreenX = Screen.width / 2;
        float centrScreenY = Screen.height / 2;
 
        switch (gameMod)
        {
            case 0:
            {
                Rect LocationButton = new Rect(new Vector2(centrScreenX - 150, centrScreenY - 50), new Vector2(300, 200));
                GUI.Box(LocationButton, ""); 
            }
            break;
        }
    }

private void InitializeDefaultScreen()
    {
        MainGame gameModStart = new MainGame();
        gameModStart.gameMod = 0;
        
        Debug.Log("D02 D03 gameMod = " + gameModStart.gameMod);
 
        ImageTracker tracker = _uiScreens[(int)InteractionManagerState.SeeBattle].GetComponent<ImageTracker>();
 
        if (!tracker)
        {
            throw new MissingComponentException(tracker.GetType().Name + " component not found!");
        }
 
        ShowPlanes(false);
        tracker.Initialize();
    }

2023.01.24 16:42:40.315 16412 18550 Info Unity D02 gameMod OnGUI = -1
2023.01.24 16:42:40.316 16412 18550 Info Unity D02 gameMod OnGUI = -1
2023.01.24 16:42:40.316 16412 18550 Info Unity D02 gameMod OnGUI = -1
2023.01.24 16:42:40.349 16412 18550 Info Unity D02 D03 gameMod = 0
2023.01.24 16:42:40.402 16412 18550 Info Unity D02 gameMod OnGUI = -1
2023.01.24 16:42:40.402 16412 18550 Info Unity D02 gameMod OnGUI = -1
2023.01.24 16:42:40.414 16412 18550 Info Unity D02 gameMod OnGUI = -1