https://developer.apple.com/documentation/uikit/app_and_envi...
https://developer.android.com/guide/components/activities/ac...
I'm not an app expert nor an expert on GNOME development either, but I got a bit sceptical when I read their app example code, python with GNOME, neither is famous for being snappy.
For the moment the Librem 5 seems to be using apps designed to work on PC desktops but at lower resolutions.