Move a top-level task to be a sub-task for a different top-level task?

Perhaps I'm mistaken, but I swear I used to be able to drag an existing task onto another existing task, "merging" them and turning the dragged task into a sub-task of the destination task. Am I mistaken?

I Googled and found threads on this sub saying this doesn't exist, but they're old. I used to be premium but I went free quite some time ago, so that may be why I thought I could in the past but can't any longer?

I could just "recreate" the current task, but I have been keeping long-running notes and appreciate having those with the accurate time tags on them, so would love to be able to merge the extant task with another.