I have long used a horizontal layout with DO in which both the folders and their file contents were shown in different columns a given horizontal segment, as shown in the attachment. But recently selecting the horizontal layout does not give me this--I get only one segment of the row. Has the program changed, or am I doing something wrong?
If you want the folder tree to come back, you can do that from the Lister menu at the top and toward the right of the window.
You can then use Settings > Set As Default Lister to save it as the way new windows should open. (Can also happen automatically when the window is closed, depending on config.)