Осталось добавить проверку на правильность сборки алфавита.

import pygame
import random

def generate_alf():
 alf = 'абвгдеёжзийклмнопрстуфхцчшщъыьэюя'
 new_text = ""
 nindex = []
 for i in range(0,len(alf)):
  nindex.append(i)

 for i in range(0,(len(alf))):
  ind = random.randint(0,len(alf)-1)
  n = nindex[ind]
  nindex[ind] = nindex[i]
  nindex[i] = n

 for i in range(0,len(alf)):
  sym = alf[nindex[i]]
  new_text = new_text[:i] + sym + new_text[i:]

 return new_text

WIDTH = 825
HEIGHT = 700
FPS = 60

WHITE = (255, 255, 255)
BLACK = (0, 0, 0)
RED = (255, 0, 0)
GREEN = (0, 255, 0)
BLUE = (0, 0, 255)

pygame.init()
screen = pygame.display.set_mode((WIDTH, HEIGHT))
f1 = pygame.font.Font(None, 36)
f2 = pygame.font.Font(None, 100)
running = True
obj_y = 0
alf = generate_alf()
alf_2 = "".ljust(50)
symbol = ""
counter_symbols = 0
while running:

    for event in pygame.event.get():
        
     if event.type == pygame.QUIT:
            running = False
    
     if event.type == pygame.MOUSEBUTTONDOWN:
            if event.button == 1:
             x = event.pos[0]//25
             symbol = alf[x]
             print(symbol)
             li = list(alf_2)
             li[counter_symbols] = symbol
             alf_2 = ''.join(li)
             counter_symbols = counter_symbols+1

     for it_1 in range(0,825,25):
      for it_2 in range(0,50,25):
       pygame.draw.rect(screen,WHITE, (it_1,it_2,24,24))
     pygame.draw.rect(screen,WHITE, (0,50,825,700))
     for i in range(0,len(alf)):
      text1 = f1.render(alf[i], False,(0, 180, 0))
      screen.blit(text1, (i*25,0))
      text2 = f1.render(alf_2[i], False,(0, 180, 0))
      screen.blit(text2, (i*25,25))
      text3 = f2.render(symbol, False,(0, 180, 0))
      screen.blit(text3, (400,400))
      
        
    pygame.display.flip()
    pygame.time.delay(250) 
pygame.quit()