Opus has no control over the Start Menu. That is part of Windows and is not something we modify or are involved with in any way (other than adding our shortcuts to it, which are just normal shortcut files in a folder).
EDIT: If you mean you're clicking shortcuts in the Start Menu which should open an Opus window, and it's opening in the background, that seems to be a bug in the Start Menu with certain pinned shortcuts. Drive roots are the one example I am aware of, and there's a workaround here: