Unity 2D restart butonu çalışmıyor

using System.Collections;
using System.Collections.Generic;
using TMPro;
using UnityEngine;
using UnityEngine.UI;
using UnityEngine.SceneManagement;

[DefaultExecutionOrder(-1)]
public class GameManager : MonoBehaviour.
{
 public static GameManager Instance { get; private set; }

 public float initialGameSpeed = 5f;
 public float gameSpeedIncrease = 0.1f;
 public float gameSpeed { get; private set; }

 [SerializeField] private Text scoreText;
 [SerializeField] private Text hiscoreText;
 [SerializeField] private Text gameOverText;
 [SerializeField] private Button retryButton;

 private Player player;
 private BarrierSpawner spawner;

 private float score;
 public float Score => score;

 private void Awake()
 {
 if (Instance != null) {
 DestroyImmediate(gameObject);
 } else {
 Instance = this;
 }
 }

 private void OnDestroy()
 {
 if (Instance == this) {
 Instance = null;
 }
 }

 private void Start()
 {
 player = FindObjectOfType<Player>();
 spawner = FindObjectOfType<BarrierSpawner>();

 NewGame();
 }

 public void GameOver()
 {
 gameSpeed = 0f;
 enabled = false;

 player.gameObject.SetActive(false);
 spawner.gameObject.SetActive(false);
 gameOverText.gameObject.SetActive(true);
 retryButton.gameObject.SetActive(true);

 UpdateHiscore();
 }

 public void NewGame()
 {
 BarrierMove[] obstacles = FindObjectsOfType<BarrierMove>();

 foreach (var obstacle in obstacles) {
 Destroy(obstacle.gameObject);
 }

 score = 0f;
 gameSpeed = initialGameSpeed;
 enabled = true;

 player.gameObject.SetActive(true);
 spawner.gameObject.SetActive(true);
 gameOverText.gameObject.SetActive(false);
 retryButton .gameObject.SetActive(false);

 UpdateHiscore();
 }

 private void Update()
 {
 gameSpeed += gameSpeedIncrease * Time.deltaTime;
 score += gameSpeed * Time.deltaTime;
 scoreText.text = Mathf.FloorToInt(score).ToString("D5");
 }

 private void UpdateHiscore()
 {
 float hiscore = PlayerPrefs.GetFloat("hiscore", 0);

 if (score > hiscore)
 {
 hiscore = score;
 PlayerPrefs.SetFloat("hiscore", hiscore);
 }

 hiscoreText.text = Mathf.FloorToInt(hiscore).ToString("D5");
 }

}

using UnityEngine;
using UnityEngine.SceneManagement;

public class RestartGame : MonoBehaviour
{
 public void Restart()
 {
 // Aktif sahnenin adını alır ve sahneyi yeniden yükler
 SceneManager.LoadScene(SceneManager.GetActiveScene().name);
 }
}

public void GameOver()
{
 gameSpeed = 0f;
 // enabled = false; // Bu satırı kaldırın.

 player.gameObject.SetActive(false);
 spawner.gameObject.SetActive(false);
 gameOverText.gameObject.SetActive(true);
 retryButton.gameObject.SetActive(true);

 UpdateHiscore();
}

public void NewGame()
{
 // Sahneyi yeniden yükleyerek oyunu yeniden başlatın.
 SceneManager.LoadScene(SceneManager.GetActiveScene().name);
}

public void GameOver()
{
 gameSpeed = 0f;
 // enabled = false; // Bu satırı kaldırın.

 player.gameObject.SetActive(false);
 spawner.gameObject.SetActive(false);
 gameOverText.gameObject.SetActive(true);
 retryButton.gameObject.SetActive(true);

 UpdateHiscore();
}

public void NewGame()
{
 // Sahneyi yeniden yükleyerek oyunu yeniden başlatın.
 SceneManager.LoadScene(SceneManager.GetActiveScene().name);
}