Hi @anon10811100, welcome to the Asana Community Forum!
I investigated this further and It’s currently not possible to see subtask indication on mobile. We are implementing some updates on mobile at the moment, for example, the new Grid view that allows you to see custom field. I’ve gone ahead and sent your feedback to our team so it can be considered in future updates. I also suggest you to upvote for this feature in this thread: The subtask / description arrow indicator on the desktop site should be on the mobile app as well