I may be blind, but I'm pretty sure that the mobile app currently lacks the ability to convert a subtask to a regular task. As well as to move a subtask to a different parent task. Stumbled upon it a few times and had no desktop client with me to change the task structure.

It seems that the previous mobile app already had at least partial support for this:

Can you reintroduce support for converting/moving subtasks on mobile?

With many things to critizise about the web app, I also wanna leave something positive - IMO the mobile app has come along nicely! Some things are missing and weird, but the overall experience and reliability has greatly improved for me.