[{readings:[{t:"temperature",r:130},{t:"humidity",r:100}],created_at:"2021-01-05T10:28:49.070Z"},{readings:[{t:"temperature",r:123},{t:"humidity",r:456}],created_at:"2021-01-05T10:32:50.727Z"}]

db.collection.aggregate([{$unwind:"$readings"},{$match:{"readings.t":"temperature"}},{"$project":{_id:0,data:["$readings.r","$created_at"]}}])