On Mac, when I check off a subtask in a recurring task, the subtask disappears. It reappears as part of the rescheduled task when the whole task is completed, but until then, there's no way to see it or "un-do" it in the current task.
On ios, the subtask just shows as checked off - and this was the way it worked on Mac until - well, I just noticed it, but I know that a few days ago, the subtask remained visible. Thus I could see what parts of a task had been completed and/or mark them as incomplete again.
Is this something that has been changed in a new release, or have I inadvertently changed a setting somewhere, or...?