Database
[{_id:ObjectId("64d69473da87c0c91ae7c596"),reviews:[{creationdate:1,val:5},{creationdate:3,val:3}]},{_id:0,reviews:[{creationdate:10,val:5}]}]
Query
db.collection.find({_id:ObjectId("64d69473da87c0c91ae7c596")},{title:1,reviews:{$concatArrays:["$reviews",{$sortArray:{input:"$reviews",sortBy:{creationdate:-1}}}]}})