[{"date":"20201005","data":[[10,20,30,40,50],[60,70,80,90,10],[11,12,13,14,15]]},{"date":"20201006","data":[[12,22,32,42,52],[61,77,88,98,10],[11,12,13,14,15]]},{"date":"20201007","data":[[11,21,31,41,51],[16,17,18,19,10],[11,12,13,14,99]]}]

db.collection.aggregate([{$unwind:"$data"},{$project:{"max":{"$max":"$data"}}},{$group:{"_id":null,"max":{$max:"$max"}}}])