[{_id:"123",status:"seen",userId:"589"},{_id:"223",status:"seen",userId:"589"},{_id:"474",status:"unseen",userId:"589"},{_id:"875",status:"seen",userId:"112"},{_id:"891",status:"unseen",userId:"112"}]

db.collection.aggregate([{$group:{_id:"$userId",totalSeen:{$sum:{$cond:[{$eq:["$status","seen"]},1,0]}},total:{$sum:1}}},{$project:{_id:0,userId:"$_id",notificationPercentage:{$multiply:[{$divide:["$totalSeen","$total"]},100]}}}])