Would like the FDB button that opens dual lister to open folder specified in the options please.
The purpose of that button is to duplicate the current folder into the dual display (and open the dual display if it isn't already open).
If you want a button that just opens the dual display in its default folder, simply add one to the toolbar. There's one in the default (main) toolbars already, although it looks like you've deleted it from yours, but you could copy or re-create it in the file display toolbar if you want it there.