@Paloma_Ibañez, That linked post is about confirming the visibility of subtasks in certain situations. It’s not about subtask sorting. Asana shows subtasks in the order you put them, so sorting/grouping applies only to the top-level tasks themselves, not subtasks.
There are several requests in Product Feedback which you can search for and add your vote to at the top of each, for example:
Thanks,
Larry