Accessing the "many" side from the "one" side effectively

Question

Considering the following models:

class ManySide(django.db.models.Model):
    one_side = models.ForeignKey(
        to=OneSide, on_delete=models.PROTECT, related_name="related_one_side"
    )

class OneSide(django.db.models:model):
    # not containing any field relevant here

    def many_side_elements(self):
        pass # ?

What should I include in method many_side_elements so that calling it from a OneSide Model instance would list a queryset of ManySide elements?

Official docs imply that given o is a OneSide isntance, o.many_side_set.all() should work but it returns an error in shell.

My current solution is the following:

from django.apps import apps

[...]

def many_side_elements(self):
    ManySideModel = apps.get_model('<app_name_here>', 'ManySide')

    val = ManySideModel.objects.filter(one_side=self)

But I'm concerned it's ineffective since it requires importing the other Model. Actually it caused a circular dependency error message in my project, hence the get_model usage.

Is there any better way? Or xy_set should work in the first place? Then what am I doing wrong?