For a task that does not yet have an existing subtask, you can create one by hovering over the task and selecting the icon below!
How to show subtasks as separate items when sorting and filtering
Flip the toggle shown below to enable subtask visibility when sorting and filtering!
Convert tasks to subtasks in List View
Utilize the Multitask Toolbar in List View to bulk-convert tasks into subtasks! Just select the purple dot next to the task/s you wish to convert and click the image shown below.