db={"books":[{"_id":{"$oid":"64ba6a416504f1f01d773faa"},"isbn":8765434567890,"booktitle":"some text",},{"_id":{"$oid":"64ba6a416504f1f01d773fab"},"isbn":8765434566666,"booktitle":"other book",}],"notes":[{"_id":{"$oid":"64ba6a416504f1f01d773faa"},"isbn":8765434567890,"note":"blabla",}]}

db.books.aggregate([/**{* "$match": {}*},*/{"$lookup":{"from":"notes","localField":"isbn","foreignField":"isbn","as":"related_note"}},{$match:{related_note:[]}},{"$project":{"isbn":"$isbn","title":"$title","note":"-- no notes about this title",}}])