I noticed that the rectangles only appeared after I closed the program/broke the loop. I realised that you misindented your code
i.e

# -------- Instruction Page Loop -----------
while done==False and display_instructions:
   
   for event in pygame.event.get(): # User did something
      
      if event.type == pygame.QUIT: # If user clicked close
         done=True # Flag that we are done so we exit this loop
         
      if event.type == pygame.MOUSEBUTTONDOWN:
            
         instruction_page += 1

         
      #instruction pages set    

  
      if instruction_page == 3:
            display_instructions = False
            
            # Set the screen background
            screen.fill(BLACK)
            
      elif instruction_page == 1:
         # Draw instructions, page 1
         # This could also load an image created in another program.
         # That could be both easier and more flexible.
               
         text=font.render("Welcome to Spatial Recall: ", True, PURPLE)
         screen.blit(text, [10, 10])
         text=font.render("The game that tests your memory!!!", True, WHITE)
         screen.blit(text, [10, 50])
         
         text=mmfont.render("Click for instructions", True, RED)
         screen.blit(text, [40, 150])

         pygame.display.update()
         screen.fill(BLACK)
      
      elif instruction_page == 2:
         # Draw instructions, page 2
         text=font.render("This is how the game goes: The", True, WHITE)
         screen.blit(text, [10, 10])
         
         text=font.render("computer is going to flash some green", True, WHITE)
         screen.blit(text, [10, 40])    
         
         text=font.render("boxes at random positions. It's", True, WHITE)
         screen.blit(text, [10, 70])       
         
         text=font.render("up to you to decide where you", True, WHITE)
         screen.blit(text, [10, 100]) 
         
         text=font.render("think they are hidden.", True, WHITE)
         screen.blit(text, [10, 130])  
         
         text=font.render("Good Luck!!.", True, PURPLE)
         screen.blit(text, [20, 180])          
         
         text=mmfont.render("PLAY GAME", True, RED)
         screen.blit(text, [120, 330])
         # Limit to 20 frames per second
         clock.tick(20)
         
         # Go ahead and update the screen with what we've drawn.
         pygame.display.flip()

This is properly indented.

Note: You can't do anything for the first 10 seconds or so
Also the text needs a update function i.e beneath the "Click for instructions" code(It's red). Plus according to my Python Shell pygame can't load wave files.

Otherwise the code is fine apart from maybe needing a win animation

P.S : Why were you doing this at 2am in the morning?


Edit: Strange, for some reason I posted 3 times.