Hi Ed, thanks for your reply.
I pulled the latest commit from the dev branch and built the Projucer. I did what you suggested:
And after “save & open in IDE” I did see my storyboard under resources in Xcode:
But the launch screen didn’t show up. It behaved exactly the same as what I described in my first post (what I did then was adding MyStoryboard.storyboard to the “Custom Xcode Resource Folders” field in the iOS exporter).
To make the storyboard work right, I need to add that storyboard manually in Xcode. But the problem is that every time when I save in the Producer, it got messed up.
@matkatmusic 's solution works for me but the only small issue is that I’ve been needing to delete the storyboard when I build the macOS app. Hope that clarifies it.