It is impossible to collapse/expand a selected folder from the
Files left hand-side pane. We can only use the
Collapse all button since version 1.0, but this affects all the folders.
Collapse folder and
Expand folder option in the context menu after pressing
RMB on a selected folder.
Use a Collapse All community plugin.
This issue has been closed, and actually, I cannot see that the hotkey has been implemented: Keyboard shortcut to collapse folders / collapse all.