[{"_id":ObjectId("62277d92a561e550d5ec73ca"),"sid":1,"sname":"sad","semail":"dsa","scourse":"it","enrolled":[{"subjid":3}]},{"_id":ObjectId("6227875bdbcc41a56a863697"),"sid":2,"sname":"daws","semail":"dws","scourse":"cs","enrolled":[{"subjid":1,"grades":[{"prelim":"A","midterm":"B","prefinal":"B","final":"A"}]},{"subjid":2,"grades":[{"prelim":"D","midterm":"A","prefinal":"B","final":"F"}]}]}]

db.collection.aggregate([{"$match":{"sid":2,"enrolled.subjid":1}},{"$addFields":{"enrolled":{"$filter":{"input":"$enrolled","as":"en","cond":{$eq:["$$en.subjid",1]}}}}},{$unwind:"$enrolled"},{$unwind:"$enrolled.grades"},{$limit:1},{$project:{_id:"$enrolled.subjid",prelim:"$enrolled.grades.prelim",midterm:"$enrolled.grades.midterm",prefinal:"$enrolled.grades.prefinal","final":"$enrolled.grades.final"}}])