STR:
Settings -> Preferences -> General -> Localization: select a RTL language (e.g. Hebrew).
Restart NPP.
Open the Document List.
Left-click the title, drag the window and try docking it on the other side or at the bottom.

Result:
The window can not be docked at the desired place.

Notepad++ v8.1.6 (32-bit)
Build time : Oct 7 2021 - 20:16:28
Path : C:---\notepad++ Original.exe
Command Line :
Admin mode : ON
Local Conf mode : ON
Cloud Config : OFF
OS Name : Windows 10 Enterprise (64-bit)
OS Version : 2009
OS Build : 19042.985
Current ANSI codepage : 1255
Plugins : ComparePlus.dll HTMLTag_unicode.dll MenuIcons.dll PythonScript.dll _CustomizeToolbar.dll