Django how to add members to groups through signals?

Using Django
1

my others signals working such as updating and creating instance but I am not understanding why it’s not adding members to group?

@receiver(post_save,sender=settings.AUTH_USER_MODEL)
def update_user_profile_from_User_model(sender,instance,created,**kwargs):
    if instance.email:
        MyAuthors.objects.filter(user=instance).update(user=instance,first_name=instance.first_name,last_name=instance.last_name,email=instance.email,is_blog_author=instance.is_blog_author)
        
        if instance.is_blog_author == True:
            my_group = Group.objects.get(name='myauthors')
            print("group name: ", my_group )
            add_user = my_group.user_set.add(instance)  
            print("add_user: ", add_user )

print result:

group name:  myauthors
add_user:  None

I also tried this but didn’t work.

group = Group.objects.get(name='myauthors')
        if instance.is_blog_author:
           instance.groups.add(group)
           instance.save()

#update1 my user model:

class UserManagement(AbstractUser):
      is_blog_author = models.BooleanField(default=False)
      is_editor = models.BooleanField(default=False)
      is_subscriber = models.BooleanField(default=False)
      is_customer = models.BooleanField(default=False)

update2
After added following changes my user added to group but not saving.

if instance.is_blog_author == True:
            User_id = get_user_model()
            user_add_to_group = User_id.objects.get(pk=instance.id)
            my_group = Group.objects.get(name='myauthors')
            print("group name: ", my_group )
            add_user = my_group.user_set.add(user_add_to_group)  
            print("add_user: ", user_add_to_group )

print result:

group name:  myauthors
add_user:  aws

how to save in signals ? I tried add_user.save() and getting this error

'NoneType' object has no attribute 'save'