Hi Marco, I'm using UIKit in Touchgram (because it was started ages ago) so can't help specifically but have spent most of the last 3 years in this space so happy to help.
Touchgram is probably the most complex iMessage app extension ever built (especially when I wrap v1.3) - it's effectively a full Keynote-level layout system plus gesture recognition plus exposing SpriteKit features such as shaders, animations & particles... all inside iMessage...to send interactive messages.
Responding to the Delete Main.Storyboard point
The result is a bank screen on the iPhone and the app icon in the middle of a blank screen on the simulator
If you are seeing that, you are launching the app from XCode.
You need to launch the Message Extension to debug it, which will bring it up inside Messages.
Note that this is very fragile - I sometimes have to launch a couple of times and do a dance of quitting XCode/Simulators.
Topic:
App & System Services
SubTopic:
General
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