When you use [Window] + [E] to open a Windows Explorer window, it opens in the two-panel layout. To have it open with a single pane by default, do the following.
1- In the Registry Editor, navigate to
2- Double-click on (Default) and change the string to
[ ViewFolder (“%1”, %I, %S)] (Including the brackets)
3- To revert to the double-pane windows, set to
[ ExploreFolder (“%1”, %I, %S)]