Well, I finally figured this out for myself. In iOS9, clicking on the latest message in a thread immediately opened an indented list of messages in that thread. In iPadOS, selecting the latest message only displays a tiny circle containing a „>“ in the uppr right of the item in the navigation pane. Clicking on this circle makes the „>“ point downward instead of to the right; then the other messages in the thread are displyed below as in iOS9, and can be individually selected for deletion. Fortunately, I have an Apple Pencil for my iPad, otherwise I would be out of luck: this tiny circle is far too small to be fingertipped, even by an infant. This is the ultimate irony: when I complained in another thread about operations I found difficult to accomplish with pencil and keyboard, I was told that the iPad was intended to be operated by fingertips. ;-{