Django Admin, custom queryset, can't groupe by (Exception Value: 'dict' object has no attribute '_meta')

[ebuild]

I have this model which map to a postgresql view

class AppModel(models.Model):
     
    nbr = models.BigIntegerField(blank=True, null=True)
    region = models.ForeignKey(AppWilaya,blank=True, null=True)
    date_preorder = models.DateField(blank=True, null=True)
    id = models.IntegerField(primary_key=True,blank=True, db_column='dummy_id')

What I want to achieve is to have region > sum(nbr), so:

class AppModelAdmin(admin.ModelAdmin):
....
def queryset(self, request):
        qs = super(AppModelAdmin, self).get_queryset(request)  
        qs=qs.values("region").annotate(total=Sum( 'nbr'))

But Django is throwing an exception:

Exception Value: 'dict' object has no attribute '_meta'
Exception Location: D:\Python335\lib\site-packages\django\contrib\admin\util.py in lookup_field, line 242

Note when I remove .values("region") the exception doesn't occure.

Am I missing something ?