[{"id":"1","answers":[{"id":"11","deletedAt":"2021-05-28T20:23:30.409Z",}]},{"id":"2","answers":[{"id":"22","deletedAt":null,}]}]

db.collection.aggregate([{"$set":{"answers":{"$filter":{"input":"$answers","cond":{$ne:["$$this.deletedAt",null]}}}}},{$match:{$expr:{$ne:["$answers",[]]}}}])