Hi lahbach, sorry for not replying sooner. I made a comprehensive test with the Splashscreen feature with all related project property combination a few days ago to make sure the Storyboard feature is working.
And yes, it doesn't work. The Splashboard image is ignored.
Adaptive icons, using
background don't work properly either. The only working one is using the
App Icon purpose, then Construct 3 will make it into a one-layered adaptive icon. However, it's not really the real deal.
If possible, you might want to consider using Android Studio or Cordova instead. You can ensure it's all working from there. There should be tutorials and documentation in the internet.