Self join within a smart folder

Unfortunately, and as we all know, in smart folders (and in list), the representation of self joins is not possible. Here is an example: project → task → subtask

As you can see, the subtask is flattened to the level of the parent task.
How can I represent projects hierarchically if I don’t have this functionality?

It works if the table in self join is placed the first level of the smart folder or list.
So the only way is to represent the project as a top-level task, but as you know the project has fields other than the task, these project-specific fields would remain empty for the records representing the tasks.

This is a problem that has been waiting for a solution for a long time.
I mainly use Fibery for knowledge management and do well, but reading that this application was born mainly for work flow and project management, I am surprised that this structural problem, which in my opinion is not insignificant, is not yet addressed.
The architecture project → subproject → task → subtask → subtask etc. is the basis for project management.
Best regards.