It's a DLL specifically for IE. BHO stands for browser helper object. Here's a MS article on them from 2007. Not sure if it'll be useful outside of IE.
Finally: _WD_Window() retrieves Window handles in this sense: https://www.w3.org/TR/webdriver/#dfn-window-handles So they are not the same as "Window handles" from MSWindowsOS and therefore cannot be used interchangeably.
Edge can only run legacy web apps / protocols in IE mode.
To get this going you need the IEDriver
See here for more info
https://docs.microsoft.com/en-gb/microsoft-edge/webdriver-chromium/ie-mode?tabs=java