[{"_id":ObjectId("5e6a82853464934e0ced4dcb"),"id_process":2,"fecha_termina":"12/03/2020 01:42:12"},{"_id":ObjectId("5e6a82803464932c4838b3fb"),"id_process":2,"fecha_termina":"12/03/2020 01:42:07"},{"_id":ObjectId("5e6a825e34649336ac628ba8"),"id_process":1,"fecha_termina":"12/03/2020 01:41:33"},{"_id":ObjectId("5e6a82593464934884a59263"),"id_process":1,"fecha_termina":"12/03/2020 01:41:28"},{"_id":ObjectId("5e6a81b93464935cf41d3455"),"id_process":1,"fecha_termina":"12/03/2020 01:38:47"}]

db.collection.aggregate([{$group:{"_id":"$id_process","fecha_termina":{"$first":"$fecha_termina"}}},{$project:{"_id":0,id_process:"$_id",fecha_termina:"$fecha_termina"}}])