If Opus is already running then the pinned icon should just open the Default Lister.
If Opus isn't already running then the pinned icon should do what's set in Preferences / Launching Opus / Startup.
(Remember that Opus continues running in the background by default.)
If that isn't the case, try fully exiting Opus, then unpin the icon, launch Opus via the Start Menu, and then re-pin the icon. Maybe the old pinned icon inherited some command-line arguments from somewhere.