How can I clean unpinned (recent) items from taskbar? The part shown here:
Assuming that you mean to remove the feature entirely:
From the *Windows Settings", you need to go to Personalization and then Start.
This gives you a window with options for turning Recent Items off:
On the other hand, if you simply wish to empty the list but leave the feature:
The list comprises shortcuts held in
%AppData%\Microsoft\Windows\Recent Items Delete them