UI buttons not detecting mouse click/mouseover

So I've implemented a pause menu following some tutorials, however the menu seems to be completely unable to detect the mouse at all, including left click.

What's 'meant' to happen is the buttons darken when hovered over, and then darken moreso when clicked on, however they just always appear dark, and nothing happens when they're clicked on.

Looking at other people with this issue I have double checked I have an Event System, and that everything's on one canvas.

I've attached some screenshots that'll hopefully help out.

Note a lot of the stuff on the UI is a fellow Student's work, so forgive the lack of organisation, I've tried disabling his components and it still doesn't work sadly.

Here's the code for the pause menu:

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 public class PauseMenu : MonoBehaviour
 {
 
     public static bool gameIsPaused = false;
 
     public GameObject pauseMenuUI;
 
     CursorLockMode desiredMode;
     
     void Update () {
         if (Input.GetKeyDown(KeyCode.Escape))
         {
             if (gameIsPaused)
                 Resume();
             else
                 Pause();
         }
     }
 
     public void Resume()
     {
         pauseMenuUI.SetActive(false);
         Time.timeScale = 1f;
         gameIsPaused = false;
         Cursor.visible = false;
         desiredMode = CursorLockMode.Confined;
     }
 
     void Pause()
     {
         pauseMenuUI.SetActive(true);
         Time.timeScale = 0f;
         gameIsPaused = true;
         Cursor.visible = true;
         desiredMode = CursorLockMode.None;
     }
 
     public void Quit()
     {
         Debug.LogWarning("Game quits if not in Unity editor");
         Application.Quit();
     }
 }