[Answered ]-Django – filter two M2M fields to one model for specifis condition happening in single object

You can use a combination of .filter(…) ^[Django-doc] and .exclude(…) ^[Django-doc] in an Exists subquery ^[Django-doc]:

from django.db.models import Exists, OuterRef

Model1.objects.filter(
    Exists(
        Model2.objects.filter(rel1=OuterRef('pk')).exclude(
            rel2=OuterRef('pk')
        )
    )
)

We thus return Model1 objects given there exists (at least one) Model2 object where that item appears in the rel1 relation, and not in the rel2 relation.