[{_id:ObjectId("633199db009be219a43ae426"),name:"Max",examScores:[{difficulty:4,score:57.9},{difficulty:6,score:62.1},{difficulty:3,score:88.5}]},{_id:ObjectId("633199db009be219a43ae427"),name:"Manu",examScores:[{difficulty:7,score:52.1},{difficulty:2,score:74.3},{difficulty:5,score:53.1}]}]

db.collection.aggregate([{"$addFields":{"relevantEntry":{$first:{$sortArray:{input:"$examScores",sortBy:{"score":-1}}}}},},{"$project":{_id:0,name:1,difficulty:"$relevantEntry.difficulty",maxScore:"$relevantEntry.score"}}])