[{"_id":1,"username":"test","user_details":{}},{"_id":2,"username":"test","user_details":{"name":"Test","addreess":"tets addr","city":"nddj"},verify_at:ISODate("2021-08-30T10:23:37.558Z")},{"_id":3,"username":"test","user_details":{"not":"empty"}},{"_id":4,"username":"test","user_details":{},verify_at:ISODate("2021-08-30T10:23:37.558Z")}]

db.collection.find({"$or":[{"user_details":{"$ne":{}}},{"$and":[{"user_details":{}},{"verify_at":{"$exists":false}}]}]})