When you use [Windows] + [E] to open a
Windows Explorer window, it opens in
the two-pane layout. To have it open
with a single pane by default, do
the following.
In the Registry Editor, navigate to
HKEY_CLASSES_ROOT\Folder\shell\
explore\ddeexec
Double-click on (Default) and
change the string to
[ViewFolder(“%l”, %I, %S)]
(including the brackets)
To revert to the double-pane window,
set (Default) to
[ExploreFolder(“%l”, %I, %S)]