[{"_id":ObjectId("5f38fb2b52e28012a8f175f9"),"date":"2020-08-16","values":{"wert1":5.0,"wert2":9.0}},/** 2*/{"_id":ObjectId("5f38fb2b52e28012a8f175fa"),"date":"2020-08-16","values":{"wert1":3.0,"wert3":10.0}}]

db.collection.aggregate([{$project:{date:1,values:{$objectToArray:"$values"}}},{$unwind:"$values"},{$group:{_id:{date:"$date",key:"$values.k"},total:{$sum:"$values.v"}}},{$group:{_id:"$_id.key",v:{$push:{$arrayToObject:[[{k:"$_id.date",v:"$total"}]]}}}},{$replaceRoot:{newRoot:{$arrayToObject:[[{k:"$_id",v:"$v"}]]}}}])