Database
[{"active":true,"endDates":["16.11.2021","27.06.2020"],"startDates":["21.10.2022","16.10.2021","09.04.2020"]}]
Query
db.collection.aggregate([{$project:{endDates:{$map:{input:"$endDates",in:{$dateFromString:{dateString:"$$this",format:"%d.%m.%Y"}}}},startDates:{$map:{input:"$startDates",in:{$dateFromString:{dateString:"$$this",format:"%d.%m.%Y"}}}}}},{$project:{dates:{$zip:{inputs:[{$reverseArray:"$startDates"},{$reverseArray:"$endDates"}],useLongestLength:true}}}}])