Hi @Mauro_Bosio and @Marcos_Villar 
This is something our team is aware of and hoping to solve as part of the general subtask redesign they’re planning to tackle later this year. In the meantime, here is the workaround I’m using in my projects: I usually create a Section called “subtasks” which I position at the bottom of my project, and I use this section to nest all subtasks that I’ve added to the project with the “Tab+P” shortcut; this way my subtasks are linked to the project, but they don’t bother me too much in my task list. I’m not sure if you’ve heard about it, but we’re about to roll out new Sections (that will be collapsable!!), so you will soon be able to collapse this Section dedicated to subtask, reducing their visibility even more! Again, I’m aware this is not an ideal situation, but I hope this workaround will help until our Team start improving subtasks!
If you have any follow-up questions, or if there is anything else I can help you with, please let me know; I’ll be more than happy to help!