Database
[{_id:{genre:"suspense"},price:10210.6,data:[{subGenre:"Thriller",flag:false},{subGenre:"jumpScare",flag:true},{subGenre:"horror",flag:false}]}]
Query
db.collection.aggregate([{$project:{price:1,subGenre:{$let:{vars:{data:{$filter:{input:"$data",cond:"$$this.flag"}}},in:{$first:"$$data.subGenre"}}}}}])