Increase Players Speed Overtime in Endless Runner? Is my Code Unoptimized?

I'm currently attempting to make a game similar to subway surfers. Currently, I'm using timescale which I now realize may be a bad idea as this is a mobile game. Here is my code.

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 using UnityEngine.UI;
 using UnityEngine.Advertisements;
 
 public class GameManager : MonoBehaviour
 {
     private const int COIN_SCORE_AMOUNT = 3;
     private const int OBSTACLE_DODGE_AMOUNT = 10;
     public static GameManager Instance { set; get; }
 
     private bool isGameStarted = false;
     private PlayerMotor motor;
 
     // UI and UI Fields
     public Text scoreText, coinText, modifierText, hiscoreText;
     public float score, coinScore, modifierScore, timeScore;
     private int lastScore;
     public int difficultyLevel = 0;
     public double TimeLevel = 0.04;
     private int maxDifficultyLevel = 20;
     private int scoreToNextLevel = 10;
     private bool isDead = false;
     public GameObject flash;
     public static bool GameIsPaused = false;
     public GameObject pauseMenuUI;
     public Button PauseButton;
     public Button ResumeButton;
 
     // Death Menu
     public Animator deathMenuAnim;
     public Text deadscoreText, deadcoinText;
 
     private void Awake()
     {
         Instance = this;
         modifierScore = 1;
         motor = GameObject.FindGameObjectWithTag("Player").GetComponent<PlayerMotor>();
         flash = GameObject.Find("Tap Anywhere to Start");
         pauseMenuUI.gameObject.SetActive(false);
         PauseButton.gameObject.SetActive(true);
 
         modifierText.text = "x" + modifierScore.ToString("0.0");
         coinText.text = coinScore.ToString("0");
         scoreText.text = scoreText.text = score.ToString("0");
 
         hiscoreText.text = PlayerPrefs.GetInt("Hiscore").ToString();
         Application.targetFrameRate = -1;
     }
     private void Update()
     {
         if (MobileInput.Instance.Tap && !isGameStarted)
         {
             isGameStarted = true;
             motor.StartRunning();
 
 
             PoolsManager.poolManager.StartGame();
 
             Time.timeScale = 1f;
             flash.SetActive(false);
         }
 
         if (isGameStarted)
         {
             // Bump the Score Up
             score += (Time.deltaTime * modifierScore);
             if (lastScore != (int)score)
             {
                 lastScore = (int)score;
                 scoreText.text = score.ToString("0");
             }
         }
         {
 
             if (isDead)
                 return;
 
             if (score >= scoreToNextLevel)
                 LevelUp();
 
             score += Time.deltaTime * difficultyLevel;
             scoreText.text = ((int)score).ToString();
         }
         void LevelUp()
         {
             if (difficultyLevel == maxDifficultyLevel)
                 return;
 
             scoreToNextLevel *= 2;
             difficultyLevel++;
             modifierScore += 1;
 
             Time.timeScale += 0.04f;
             timeScore += 0.04f;
         }
     }
 
     public void GetCoin()
     {
         coinScore++;
         coinText.text = coinScore.ToString("0");
         score += COIN_SCORE_AMOUNT;
         scoreText.text = scoreText.text = score.ToString("0");
     }
 
     public void DodgeObstacle()
     {
         score += OBSTACLE_DODGE_AMOUNT;
         scoreText.text = scoreText.text = score.ToString("0");
     }
 
     public void UpdateModifier(float modifierAmount)
     {
         modifierScore = 1.0f + modifierAmount;
         modifierText.text = "x" + modifierScore.ToString("0.0");
     }
 
     public void OnPlayButton()
     {
         UnityEngine.SceneManagement.SceneManager.LoadScene("Hallway Dash");
     }
 
     public void OnMenuButton()
     {
         UnityEngine.SceneManagement.SceneManager.LoadScene("Menu");
         Time.timeScale = 1f;
     }
 
     public void OnDeath()
     {
         FindObjectOfType<AudioManager>().Play("Death");
         isDead = true;
         deadscoreText.text = score.ToString("0");
         deadcoinText.text = coinScore.ToString("0");
         deathMenuAnim.SetTrigger("Dead");
         modifierScore = 0f;
 
         if (score > PlayerPrefs.GetInt("Hiscore"))
         {
             float s = score;
             if (s % 1 == 0)
                 s += 1;
             PlayerPrefs.SetInt("Hiscore", (int)score);
         }
     }
 
     public void Resume()
     {
         pauseMenuUI.SetActive(false);
         Time.timeScale = timeScore;
         GameIsPaused = false;
         PauseButton.gameObject.SetActive(true);
         pauseMenuUI.gameObject.SetActive(false);
     }
 
     public void Pause()
     {
         pauseMenuUI.SetActive(true);
         Time.timeScale = 0f;
         GameIsPaused = true;
         PauseButton.gameObject.SetActive(false);
         pauseMenuUI.gameObject.SetActive(true);
     }
 }