db={"products":[{"_id":"61b823681975ba537915cb0c","salesInfo":{"_id":"61b823681975ba537915c23c","salesDate":[{"_id":"61b3aa4a7b04b30cd0a76b06","salesQuantity":100,"soldPieces":36,"holdPieces":0},{"_id":"61b3aa4a7b04b30cd0a75506","salesQuantity":100,"soldPieces":36,"holdPieces":0}]}}]}

db.products.aggregate([{$addFields:{"salesInfo.salesDate":{"$map":{"input":"$salesInfo.salesDate","as":"s","in":{"_id":"$$s._id","salesQuantity":"$$s.salesQuantity","soldPieces":"$$s.soldPieces","holdPieces":"$$s.holdPieces","percentageSold":{$divide:[{$add:["$$s.soldPieces","$$s.holdPieces"]},{$multiply:["$$s.salesQuantity",100]}]}}}}}}])