Database
[{"_id":"2023-04-08","dailyNotes":[{"therapyDiscipline":"PT","individual":[60,45,30,75,55]},{"therapyDiscipline":"YT","individual":[2,4]}]}]
Query
db.collection.aggregate([{$project:{_id:1,dailyNotes:{$reduce:{input:"$dailyNotes",initialValue:[],in:{$concatArrays:["$$value",[{individual:{$sum:"$$this.individual"}}]]}}}}}])