You can start with this:
from django.apps import AppConfig

class YourAppConfig(AppConfig):
    name = 'your_app'

    def ready(self):
        import your_app.signal

Next part more debug tool:

@receiver(post_save, sender=User)
def create_profile(sender, instance, created, **kwargs): 
    user = instance
    print("User pk:", user.pk)
    print("Created flag:", created)
    
    if created: 
        print('A new user is created')
    else: 
        print('A new user is not created')
    
    print(sender, user, created)

Do you use bulk_create?