[{"_id":{"Shop":"FirstShopNameCovered"},"isLinkedTo":[{"PERSON":"Carleen","CITY":"Rome","ROOM":"Kitchen","STYLEPREFERED":"Modern","hasDonated":{"DATE":"2019-10-11","OBJECT":"Set of dishes","COST":72,"COLOR":"White","PAYMENT":"Credit card"}},{"PERSON":"Carleen","CITY":"Rome","ROOM":"Kitcher","STYLEPREFERED":"Modern","hasDonated":{"DATE":"2018-10-26","OBJECT":"Set of chairs","COST":353,"COLOR":"Grey","PAYMENT":"Coupon"}},{"PERSON":"Pernick","CITY":"Venezia","ROOM":"Bathroom","STYLE":"Minimalist","hasDonated":{"DATE":"2018-09-18","OBJECT":"Mirror","COST":68,"COLOR":"Brown","PAYMENT":"Credit card"}}]}]

db.collection.aggregate([{"$unwind":"$isLinkedTo"},{$group:{_id:{_id:"$_id",per:"$isLinkedTo.PERSON"},isLinkedTo:{$first:{PERSON:"$isLinkedTo.PERSON",CITY:"$isLinkedTo.CITY",ROOM:"$isLinkedTo.ROOM",STYLEPREFERED:"$isLinkedTo.STYLEPREFERED"}},hasDonated:{$addToSet:"$isLinkedTo.hasDonated"}}},{$addFields:{_id:"$_id._id","isLinkedTo.hasDonated":"$hasDonated"}},{$project:{hasDonated:0}},{$group:{_id:"$_id",isLinkedTo:{$push:"$isLinkedTo"}}}])