Django order by number of related objects in class Meta

In Django, i want to set the default model ordering to be by the number of related objects. In my case i would like to order the objects by the number of likes, where likes is a ManyToManyField of users that have liked the post:

class Post(models.Model):
    likes = models.ManyToManyField(User)

    class Meta:
        ordering = []  # What can i put here?

The common solution seems to be django aggregation:

from django.db.models import Count

top_posts = Post.objects.annotate(num_likes=Count('likes')).order_by('-num_likes')

But this is called on the queryset, and doesn't seem like an option when defining the model.

class PostManager(models.Manager):
    def get_queryset(self, *args, **kwargs):
        return (
            super()
            .get_queryset(*args, **kwargs)
            .alias(num_likes=Count('likes'))
            .order_by('-num_likes')
        )


class Post(models.Model):
    likes = models.ManyToManyField(User)

    objects = PostManager()