Database
[{"_id":"A1","Price":{"2020-08-25":{"P":[1200,1300,1250]},"2020-08-26":{"P":[1310,1400,1200]},"2020-08-27":{"P":[1500,1300,1300]},}},{"_id":"A2","Price":{"2020-08-25":{"P":[1200,1300,1250]},"2020-08-26":{"P":[1310,1400,1200]},"2020-08-27":{"P":[1500,1300,1300]},}}]
Query
db.collection.aggregate([{$project:{"prices":{"$objectToArray":"$Price"}}},{$group:{"_id":null,P:{$addToSet:{$max:"$prices.v.P"}}}},{$project:{"maxPrice":{$max:{$first:"$P"}}}}])