Database
[{owner:2,bids:[{amount:36,date:"2021-06-23T21:00:00.000+00:00",placedBy:10},{amount:16,date:"2021-06-23T21:00:00.000+00:00",placedBy:20}]}]
Query
db.collection.aggregate([{$project:{"bids":{"$map":{"input":"$bids","in":{amount:"$$this.amount",date:"$$this.date",placedBy:{$cond:[{"$eq":["$owner",1]},"$$this.placedBy","$$REMOVE"]}}}}}}])