I have a search box but when I type the task name in there, the one I want is not a choice in the list at all. How is this populated? I have so many tasks that the idea of not being able to use the “convert to subtask of…” function is unreasonably slow.
I have something radical that always work: go to the target task, copy the URL (using the icon), and then go back to your task → in the search paste the link, it will offer to choose the task.
This autocomplete is hard to use if you have many tasks with similar names.