[{"_id":{"$oid":"60d635cb26bec4004fb19341"},"section":"Mi Tiempo","createdAt":ISODate("2021-06-25T20:00:11.668+00:00"),"_v":0}]

db.collection.aggregate([{"$match":{$expr:{"$regexMatch":{"input":{"$toString":"$createdAt"},"regex":"2021-06-25T"}}}}])