Wrangling Targets in Xcode - "Select app to run"

I've added a new target to my macOS project -- a quicklook preview extension. Now, when I try to build the project, I get a dialog saying "Select App to Run".

QuickLook Simulator launches, but my app doesn't build -- by which I mean it doesn't attempt to build.

What do I have to do to build the whole thing?

OK, I need to change the Scheme, under Product menu, to get the app to build again. I was having a nightmare with build settings, but that seems to have calmed down.

Wrangling Targets in Xcode - "Select app to run"
 
 
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