[{"_id":1,"name":"John",items:{"123wda1":{"type":"car","qty":"2"},"123wda2":{"type":"boat","qty":"2"}}},{"_id":2,"name":"Jane",items:{"567wda1":{"type":"plane","qty":"1"},"567wda2":{"type":"car","qty":"1"}}}]

db.collection.aggregate([{$project:{items1:{$objectToArray:"$items"}}},{$unwind:"$items1"},{"$addFields":{"typeQ":"$items1.v.type","qtyQ":"$items1.v.qty"}},{"$group":{"_id":"$typeQ","total":{"$sum":{$toInt:"$qtyQ"}}}}])