Scenes overlap in Game view in Editor and Game is stuck in Main menu after installing in mobile.

Hi. I'm made a pong Android game for practice. There are two scenes, Menu and Game. In the game view, both scenes are playing at the same time. Once I click the Play button, my UI button to change scene, the menu scene disappears and the game is playing.

And I dont know whether this is the reason, but after I build the game and install in my android mobile, the game starts, Unity logo is working and then when Menu scene started playing, the game gets stuck. The Play and Quit UI buttons are no longer working, even though they worked fine in the Editor Game view.

(I made a separate UI button app which when clicked, closes the app. It is working fine in my mobile. So, the input method is working.)

This is the code I used to change from Menu scene to Game scene.

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 using UnityEngine.UI;
 using UnityEngine.SceneManagement;
 
 public class MainMenu : MonoBehaviour
 {    
     public void PlayGame()
     {
         SceneManager.LoadScene("Game");
     }
 
     public void QuitGame()
     {
         Application.Quit();
     }
 }

Please tell me what can be the issue, this is the only code that handles scene change. Thanks in advance.

This is how it looks in the Game view, with both Menu and Game scenes overlapping.