[{deliveryDay:"2021-01-14",plate:{name:"pasta",quantity:1}},{deliveryDay:"2021-01-16",plate:{name:"pasta",quantity:3}},{deliveryDay:"2021-01-16",plate:{name:"pizza",quantity:2}}]

db.collection.aggregate([{$group:{_id:{dDate:"$deliveryDay",name:"$plate.name"},v:{$sum:"$plate.quantity"}}},{$group:{_id:"$_id.name",array:{$push:{k:"$_id.dDate",v:"$v"}}}},{$addFields:{array:{$concatArrays:[[{k:"plate",v:{name:"$_id"}}],"$array"]}}},{$replaceRoot:{newRoot:{$arrayToObject:"$array"}}}])