Database
[{_id:ObjectId("5a934e000102030405000000"),events:[{status:0,timestamp:ISODate("2022-05-29T13:26:00Z")},{status:8,timestamp:ISODate("2022-05-29T14:41:00Z")},{status:4,timestamp:ISODate("2022-05-31T10:13:00Z")},{status:3,timestamp:ISODate("2022-05-31T10:18:00Z")}]}]
Query
db.collection.aggregate([{$project:{events:{$reduce:{input:"$events",initialValue:[],in:{$concatArrays:["$$value",[{$mergeObjects:["$$this",{arrayIndex:{$size:"$$value"}}]}]]}}}}}])