When the NotePerformer mixer window is open it stays in front of Dorico. One would think that you could click on Dorico and it would come to the front. The only solution I’ve found is to minimize the NotePerformer mixer window to the Dock. Am I missing something?
The VST plug-in windows belong to the VST Audio Engine process, not Dorico itself.
On a Mac, you can use Mission Control (for me, a four?-finger swipe up), which shows you all the windows of all the apps. You’ll see the Noteperformer window separately from those of Dorico.
There is also a command which you can assign a key shortcut to, which will show the VST window for the selected item (even in Write mode!)