[{"_id":ObjectId("60f3fdae2367163726c6716b"),"username":"Johnny65","first_name":"Thaddeus","last_name":"Lueilwitz","email":"example@gmail.com","mobile":"834XXXX","profile_photo":"http://placeimg.com/640/480","login_type":2,"maps_created":ISODate("2020-04-08T20:00:28.453Z"),"created_date":ISODate("2021-06-24T16:19:07.010Z"),"favorite_lists":[{"maps":[],"name":"name 1","created_date":ISODate("2021-07-20T13:27:56.050Z")},{"maps":[],"name":"name 2","created_date":ISODate("2021-07-20T13:31:21.985Z")},{"maps":[],"name":"name 3","created_date":ISODate("2021-07-20T13:35:32.959Z")}]}]

db.collection.update({"favorite_lists.name":"name 2"},{$addToSet:{"favorite_lists.$.maps":{$each:["value 1","value 2"]}}})