How to implement extended auth-User model in SignUp form in Django?

I want to add more fields in auth-User model. So, according to this docs(https://docs.djangoproject.com/en/3.2/topics/auth/customizing/#extending-the-existing-user-model) I created a ‘UserProfile’ model in one-to-one relation with auth-user. But it’s not working in forms.py. Actually, I couldn’t implement it in forms.py

Here is my code:

models.py

class UserProfile(models.Model):
    user = models.OneToOneField(User, related_name="userprofile", on_delete=models.CASCADE)
    profile_picture = models.ImageField()

forms.py

class CustomSignupForm(SignupForm):
    profile_picture = forms.ImageField()
 
    def signup(self, request, user):
        up = user.userprofile
        user.userprofile.profile_picture = self.cleaned_data['profile_picture']
        up.profile_picture = self.cleaned_data['profile_picture']
        user.save()
        up.save()
        return user

Even after SignUp I don’t get any object in ‘UserProfile’.