Pygame won't display volume control

I'm making a game in Pygame running in Python 3.10 and the lastest version of pygame, and I can't get to display a volume control for the background music . The music is played correctly, but there is no volume control

import pygame
import random

# Initialize Pygame
pygame.init()
screen = pygame.display.set_mode((800, 600))
pygame.display.set_caption("Genesis Breaker: Legioss Shmup")
clock = pygame.time.Clock()

# Colors
WHITE = (255, 255, 255)
BLACK = (0, 0, 0)

# MUSICA 

pygame.mixer.init()
music_list = ["Space Life.mp3", "The Future is coming.mp3", "Danger Sector.mp3"]
current_music = random.choice(music_list)
pygame.mixer.music.load(current_music)
pygame.mixer.music.set_volume(0.5)  # 50% volume
pygame.mixer.music.play(-1)  # Loop indefinitely

music_volume = 0.5  # Initial volume (50%)
volume_display_timer = 0  # Timer for volume display

pygame.mixer.music.set_volume(music_volume)

for event in pygame.event.get():
    if event.type == pygame.QUIT:
        running = False

if event.type == pygame.KEYDOWN:
    if event.key == pygame.K_f:
        bullets.extend(legioss.shoot())
    elif event.key == pygame.K_PLUS or event.key == pygame.K_EQUALS:  # + or = key
        music_volume = min(music_volume + 0.1, 1.0)
        pygame.mixer.music.set_volume(music_volume)
        volume_display_timer = pygame.time.get_ticks()
    elif event.key == pygame.K_MINUS:  # - key
        music_volume = max(music_volume - 0.1, 0.0)
        pygame.mixer.music.set_volume(music_volume)
        volume_display_timer = pygame.time.get_ticks()

    elif event.key == pygame.K_PAGEUP:  # Page Up
        music_volume = min(music_volume + 0.1, 1.0)
        pygame.mixer.music.set_volume(music_volume)
        volume_display_timer = pygame.time.get_ticks()
    elif event.key == pygame.K_PAGEDOWN:  # Page Down
        music_volume = max(music_volume - 0.1, 0.0)
        pygame.mixer.music.set_volume(music_volume)
        volume_display_timer = pygame.time.get_ticks()

font = pygame.font.SysFont('arial', 24)

volume_bg = pygame.Surface((120, 60), pygame.SRCALPHA)
volume_bg.fill((0, 0, 0, 100))
screen.blit(volume_bg, (5, 165))
pygame.draw.rect(screen, (255, 0, 0), (10, 200, 100, 20), 1)
pygame.draw.rect(screen, WHITE, (10, 200, 100, 20), 2)
pygame.draw.rect(screen, (0, 255, 0), (12, 202, 96 * music_volume, 16))
volume_instruction = font.render("Usa PgUp/PgDn para ajustar volumen", True, WHITE)
screen.blit(volume_instruction, (10, 220))
if pygame.time.get_ticks() - volume_display_timer < 2000:
    volume_text = font.render(f"Volumen: {int(music_volume * 100)}%", True, WHITE)
    screen.blit(volume_text, (10, 170))

##################### FIN MUSICA ##########################################################

legioss_fighter = pygame.image.load("legioss_fighter.png")
legioss_fighter = pygame.transform.scale(legioss_fighter, (80, 100))

legioss_diver = pygame.Surface((64, 64))
legioss_diver.fill((100, 255, 100))  # Green for Diver
legioss_soldier = pygame.Surface((64, 64))
legioss_soldier.fill((255, 100, 100))  # Red for Soldier
tread_bomber = pygame.Surface((128, 64))
tread_bomber.fill((200, 200, 200))  # Gray for Bulldog

invid_frames = [
    pygame.transform.scale(pygame.image.load("invid1.png").convert_alpha(), (72, 72)),
    pygame.transform.scale(pygame.image.load("invid2.png").convert_alpha(), (72, 72)),
    pygame.transform.scale(pygame.image.load("invid3.png").convert_alpha(), (72, 72))
]

    
background_img = pygame.image.load("starfield.png")
background_img = pygame.transform.scale(background_img, (800, 1200))

napalm_img = pygame.Surface((32, 32))
napalm_img.fill((255, 150, 0))  # Orange for napalm

# Classes
class Legioss:
    def __init__(self):
        self.collision_timer = 0
        self.modes = [legioss_fighter, legioss_diver, legioss_soldier]
        self.mode = 0
        self.image = self.modes[self.mode]
        #self.rect = self.image.get_rect(topleft=(400, 500))
        self.rect = self.image.get_rect(topleft=(400, 400))
        self.speed = 6
        self.shoot_delay = 0
        self.tread_active = False
        self.tread_timer = 0
        self.energy = 100
        self.energy_timer = pygame.time.get_ticks()

    def move(self):
        keys = pygame.key.get_pressed()
        if keys[pygame.K_LEFT] and self.rect.x > 0:
            self.rect.x -= self.speed
        if keys[pygame.K_RIGHT] and self.rect.x < 800 - self.rect.width:
            self.rect.x += self.speed
        if keys[pygame.K_UP] and self.rect.y > 0:  # Changed from 300 to 0
            self.rect.y -= self.speed
        if keys[pygame.K_DOWN] and self.rect.y < 600 - self.rect.height:
            self.rect.y += self.speed
        if keys[pygame.K_SPACE] and pygame.time.get_ticks() - self.shoot_delay > 500 and self.energy >= 20:
            self.mode = (self.mode + 1) % 3
            self.image = self.modes[self.mode]
            self.rect = self.image.get_rect(center=self.rect.center)
            self.shoot_delay = pygame.time.get_ticks()
            self.energy -= 20
        if keys[pygame.K_t] and not self.tread_active and pygame.time.get_ticks() - self.tread_timer > 15000 and self.energy >= 50:
            self.tread_active = True
            self.tread_timer = pygame.time.get_ticks()
            self.energy -= 50
##        if pygame.time.get_ticks() - self.energy_timer > 1000:
##            self.energy = min(self.energy + 5, 100)
##            self.energy_timer = pygame.time.get_ticks()

    def shoot(self):
        if self.mode == 2:
            return [Bullet(self.rect.centerx - 10, self.rect.top), Bullet(self.rect.centerx + 10, self.rect.top)]
        return [Bullet(self.rect.centerx, self.rect.top)]

    def draw(self, surface):
        surface.blit(self.image, self.rect)
        if self.tread_active:
            tread_rect = tread_bomber.get_rect(center=(self.rect.centerx, self.rect.centery + 30))
            surface.blit(tread_bomber, tread_rect)
            if pygame.time.get_ticks() - self.tread_timer > 5000:
                self.tread_active = False
                return Napalm(self.rect.centerx, self.rect.top)
        return None

class Enemy:
    def __init__(self):
        self.frames = invid_frames
        self.frame_index = 0
        self.image = self.frames[self.frame_index]
        self.rect = self.image.get_rect(topleft=(random.randint(0, 800 - 30), -50))
        self.speed = 3
        self.move_timer = pygame.time.get_ticks()
        self.direction = random.choice([-1, 1])
        self.frame_timer = pygame.time.get_ticks()

    def move(self):
        self.rect.y += self.speed
        if pygame.time.get_ticks() - self.move_timer > 1000:
            self.rect.x += self.direction * 2
            if self.rect.x < 0:
                self.rect.x = 0
                self.direction = 1
            elif self.rect.x > 800 - self.rect.width:
                self.rect.x = 800 - self.rect.width
                self.direction = -1
            self.move_timer = pygame.time.get_ticks()
        if pygame.time.get_ticks() - self.frame_timer > 200:
            self.frame_index = (self.frame_index + 1) % len(self.frames)
            self.image = self.frames[self.frame_index]
            self.frame_timer = pygame.time.get_ticks()
        if self.rect.y > 600:
            self.rect.y = -50
            self.rect.x = random.randint(0, 800 - 30)

    def draw(self, surface):
        surface.blit(self.image, self.rect)

class Bullet:
    def __init__(self, x, y):
        self.rect = pygame.Rect(x - 2, y, 5, 10)
        self.speed = -15

    def move(self):
        self.rect.y += self.speed
        if self.rect.y < 0:
            return False
        return True

    def draw(self, surface):
        pygame.draw.rect(surface, (255, 0, 0), self.rect)

class Napalm:
    def __init__(self, x, y):
        self.image = napalm_img
        self.rect = self.image.get_rect(center=(x, y))
        self.speed = -10
        self.damage = 5

    def move(self):
        self.rect.y += self.speed
        if self.rect.y < 0:
            return False
        return True

    def draw(self, surface):
        surface.blit(self.image, self.rect)

game_over = False

# Game setup
legioss = Legioss()
enemies = [Enemy() for _ in range(5)]
bullets = []
napalms = []
bg_y = 0
bg_speed = 3
score = 0
font = pygame.font.Font(None, 36)

# Main loop
running = True
while running:
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            running = False
        if event.type == pygame.KEYDOWN and event.key == pygame.K_f:
            bullets.extend(legioss.shoot())

    # Update
    if not game_over:
        bg_y = (bg_y + bg_speed) % 1200
        legioss.move()
        napalm = legioss.draw(screen)
        if napalm:
            napalms.append(napalm)
        for enemy in enemies:
            enemy.move()
        bullets = [bullet for bullet in bullets if bullet.move()]
        napalms = [napalm for napalm in napalms if napalm.move()]
        for bullet in bullets[:]:
            for enemy in enemies[:]:
                if bullet.rect.colliderect(enemy.rect):
                    bullets.remove(bullet)
                    enemies.remove(enemy)
                    enemies.append(Enemy())
                    score += 10
                    break
        for napalm in napalms[:]:
            for enemy in enemies[:]:
                if napalm.rect.colliderect(enemy.rect):
                    enemies.remove(enemy)
                    enemies.append(Enemy())
                    score += 50
                    break

        if pygame.time.get_ticks() - legioss.collision_timer > 500:
            for enemy in enemies:
                if enemy.rect.colliderect(legioss.rect):
                    legioss.energy = max(0, legioss.energy - 10)
                    legioss.collision_timer = pygame.time.get_ticks()
                break

        if legioss.energy <= 0:
            game_over = True
            pygame.mixer.music.stop()

    if game_over:

        game_over_bg = pygame.Surface((600, 200), pygame.SRCALPHA)
        game_over_bg.fill((0, 0, 0, 220))  # Más opaco y grande
        screen.blit(game_over_bg, (100, 75))  # Centrado horizontalmente
        game_over_font = pygame.font.SysFont('consolas', 64)
        game_over_text = game_over_font.render("Game Over", True, WHITE)
        screen.blit(game_over_text, (250, 125))  # Centrado en el rectángulo

        pygame.display.update()

    #bg_y = (bg_y + bg_speed) % 1200
    screen.blit(background_img, (0, bg_y - 1200))
    screen.blit(background_img, (0, bg_y))
    fade = pygame.Surface((800, 20), pygame.SRCALPHA)
    for y in range(20):
        alpha = int(50 * (y / 20))  # Max alpha 50
        pygame.draw.line(fade, (0, 0, 0, alpha), (0, y), (800, y))
    screen.blit(fade, (0, 0))
    flipped_fade = pygame.transform.flip(fade, False, True)
    screen.blit(flipped_fade, (0, 580))
    # Draw
    for enemy in enemies:
        enemy.draw(screen)
    for bullet in bullets:
        bullet.draw(screen)
    for napalm in napalms:
        napalm.draw(screen)
    legioss.draw(screen)
    score_text = font.render(f"Score: {score}", True, WHITE)
    energy_text = font.render(f"Energy: {legioss.energy}", True, WHITE)
    screen.blit(score_text, (10, 10))
    screen.blit(energy_text, (10, 50))

    pygame.display.flip()
    clock.tick(60)

pygame.quit()