Hi again @Joao_Almeida
Sorry about the confusion here. I can confirm that this is currently the expected behaviour. Let me explain you why.
By default, subtasks do not automatically inherit the project from their parent task, reason why you are not seeing them in your project calendar. You will need to manually add a subtask to the project - try using the “Tab+P” shortcut to see them in your Project Calendar.
You can read more about it in the following guide article: https://asana.com/guide/help/tasks/subtasks#gl-subtask-project
This is a popular topic in the Forum and there is an existing thread requesting this functionality. If you haven’t yet, I would encourage you to cast your comment and vote: Allow to automatically add subtasks to project
Please let me know if you have any follow-up question!