Pausing the game after player gets destroyed

Hey guys, as the title says, I want to make it so that when the player game object gets destroyed, the game will then pause and bring up a screen (I’ve made one called GameOverScreen), however, I cannot seem to get my head around it. Here is my code:
using UnityEngine;
using UnityEngine.UI;

public class PlayerHealth : MonoBehaviour
{
    public float m_StartingHealth = 100f;               // The amount of health each tank starts with.
    public Slider m_Slider;                             // The slider to represent how much health the tank currently has.
    public Image m_FillImage;                           // The image component of the slider.
    public Color m_FullHealthColor = Color.green;       // The color the health bar will be when on full health.
    public Color m_ZeroHealthColor = Color.red;         // The color the health bar will be when on no health.
    public GameObject m_ExplosionPrefab;                // A prefab that will be instantiated in Awake, then used whenever the tank dies.
    public Camera mainCamera;
    public Camera gameOverCamera;
    public GameObject GameOverMenu;

    private bool gameover = false;
    private AudioSource m_ExplosionAudio;               // The audio source to play when the tank explodes.
    private ParticleSystem m_ExplosionParticles;        // The particle system the will play when the tank is destroyed.
    private float m_CurrentHealth;                      // How much health the tank currently has.
    private bool m_Dead;                                // Has the tank been reduced beyond zero health yet?

    void Start()
    {
        GameOverMenu.SetActive(false);
    }

    private void Awake()
    {
        // Instantiate the explosion prefab and get a reference to the particle system on it.
        m_ExplosionParticles = Instantiate(m_ExplosionPrefab).GetComponent<ParticleSystem>();

        // Get a reference to the audio source on the instantiated prefab.
        m_ExplosionAudio = m_ExplosionParticles.GetComponent<AudioSource>();

        // Disable the prefab so it can be activated when it's required.
        m_ExplosionParticles.gameObject.SetActive(false);
    }


    private void OnEnable()
    {
        // When the tank is enabled, reset the tank's health and whether or not it's dead.
        m_CurrentHealth = m_StartingHealth;
        m_Dead = false;

        // Update the health slider's value and color.
        SetHealthUI();
    }


    public void TakeDamage(float amount)
    {
        // Reduce current health by the amount of damage done.
        m_CurrentHealth -= amount;

        // Change the UI elements appropriately.
        SetHealthUI();

        // If the current health is at or below zero and it has not yet been registered, call OnDeath.
        if (m_CurrentHealth <= 0f && !m_Dead)
        {
            OnDeath();
            mainCamera.transform.parent = null;
            mainCamera.enabled = true;
            gameOverCamera.enabled = false;

            if (m_CurrentHealth <= 0f && !m_Dead)
            {
                gameover = !gameover;
            }
            gameover = !gameover;

            if (gameover)
            {
                GameOverMenu.SetActive(true);
                Time.timeScale = 0;
            }

            if (!gameover)
            {
                GameOverMenu.SetActive(false);
                Time.timeScale = 1;
            }
        }
    }


    private void SetHealthUI()
    {
        // Set the slider's value appropriately.
        m_Slider.value = m_CurrentHealth;

        // Interpolate the color of the bar between the choosen colours based on the current percentage of the starting health.
        m_FillImage.color = Color.Lerp(m_ZeroHealthColor, m_FullHealthColor, m_CurrentHealth / m_StartingHealth);
    }


    private void OnDeath()
    {
        // Set the flag so that this function is only called once.
        m_Dead = true;

        // Move the instantiated explosion prefab to the tank's position and turn it on.
        m_ExplosionParticles.transform.position = transform.position;
        m_ExplosionParticles.gameObject.SetActive(true);

        // Play the particle system of the tank exploding.
        m_ExplosionParticles.Play();

        // Play the tank explosion sound effect.
        m_ExplosionAudio.Play();

        // Turn the tank off.
        gameObject.SetActive(false);
    }
}

You’re toggling gameover twice with the same condition on TakeDamage which means it is never actually getting changed.

Remove:

    if (m_CurrentHealth <= 0f && !m_Dead)
    {
        gameover = !gameover;
    }

I’d also use an else condition to check the state of gameover as there’s no need to check it twice.

         if (gameover)
         {
             GameOverMenu.SetActive(true);
             Time.timeScale = 0;
         } 
         else
         {
             GameOverMenu.SetActive(false);
             Time.timeScale = 1;
         }

However I don’t know why you are trying to reset the timeScale and GameOverMenu from there since it is only going to be called when the tank is dead anyway. If you were trying to use OnDeath() to set the state of m_Dead then that’s not going to work as TakeDamage will finish executing before it runs.

You should probably move m_Dead = true; from OnDeath() to the health check within TakeDamage or just roll the two functions into one and put the explosion particles and audio in TakeDamage.