@Amir3 yes, you can create subtasks through the CSV Import. One common error I have seen is where people associate a section/column to a subtask. This supersedes any “subtask of” associations and makes the intended subtask a parent task. You can learn more about this and other importing tips in this post: 🔑 3 Key Reminders when using the CSV Importer
If this doesn’t resolve your issue, you can PM me a sample file and I can test on my end then point you in the right direction! 