I made a QUICK ACCESS TOOLBAR shortcut for "Clear search history"; here's how:
•"Search" tab doesn't show by default, so type anything in search & "Enter" to make the tab appear...
•"Recent Searches" button shows up under "Search" tab; left-click "Recent searches", then right-click "Clear search history" and choose "Add to Quick Access Toolbar"...
Now you can click the Clear Search History button (clock with red 'X') on any explorer window's Quick Access Toolbar. It doesn't actually show the history as cleared until you open a new explorer window. Like most of my "solutions" to Window's 10 issues, it's kind of a lame work-around, but still easier than waiting for Microsoft to come up with a real fix.
I hope this helps someone!