[{"_id":ObjectId("61868aa03b2fe72b58c891a5"),"name":"Max","examScores":[{"difficulty":4,"score":57.9},{"difficulty":6,"score":62.1},{"difficulty":3,"score":88.5}]},{"_id":ObjectId("61868aa03b2fe72b58c891a6"),"name":"Manu","examScores":[{"difficulty":7,"score":52.1},{"difficulty":2,"score":74.3},{"difficulty":5,"score":53.1}]}]

db.collection.aggregate([{"$project":{"_id":0,"name":1,"maxExams":{"$reduce":{"input":"$examScores","initialValue":[-1,-1],"in":{"$switch":{"branches":[{"case":{"$gte":["$$this.score",{"$arrayElemAt":["$$value",0]}]},"then":{"$concatArrays":[["$$this.score"],[{"$arrayElemAt":["$$value",0]}]]}},{"case":{"$gte":["$$this.score",{"$arrayElemAt":["$$value",1]}]},"then":{"$concatArrays":[[{"$arrayElemAt":["$$value",0]}],["$$this.score"]]}}],"default":"$$value"}}}}}}])