[{"subject":"Hello there","events":[{"status":"opened","date":"2020-01-01 17:35:31.229Z"},{"status":"clicked","date":"2020-01-02 17:35:31.229Z"},]}]

db.collection.aggregate([{$addFields:{latestEvent:{$reduce:{input:"$events",initialValue:{status:null,date:0},in:{$mergeObjects:["$$value",{$cond:[{$gt:[{$toDate:"$$this.date"},{$toDate:"$$this.value"}]},"$$this","$$value"]}]}}}}}])