[{"_id":"00000001","category":"Weather","city":"Salt Lake City","date":{"$date":{"$numberLong":"1663236000000"}},"logs":{"2022-09-14 12:00:00":{"temp":55,"humidity":25},"2022-09-14 14:00:00":{"temp":65,"humidity":35}}}]

db.collection.aggregate([{$match:{_id:{$exists:true}}},{$set:{logs:{"$objectToArray":"$logs"}}},{$set:{logs:{$map:{input:"$logs",in:{k:"$$this.k",v:{$concat:[{$toString:"$$this.v.temp"},", ",{$toString:"$$this.v.humidity"}]}}}}}},{$set:{logs:{$arrayToObject:"$logs"}}}])