Thank you @ma. Actually, I published an update yesterday, and indeed the review process went smoothly. However, I spotted an issue.
I first generated the various assets using your script here: https://github.com/distriqt/AIR-ImageScripts/
(I used a MacOS VM as I work on Windows)
I then opened the launchscreen.storyboardc file on the Mac, asking to show contents. I copied these contents onto my PC, into a local "LaunchScreen.storyboardc" directory. I then added this directory to my ADT command line, to include it to the build. I opened the generated IPA, and the "LaunchScreen.storyboardc" folder is there.
I also added this key to my XML app descriptor, in the iPhone section:
However, when I launch the app, I get a white blank screen, which is not what I want (I created actually a plain black storyboard). So I'm not sure what I'm doing wrong here. If I remove the launchscreen.storyboardc file entirely from the command line, I still get the white screen, so I'm wondering if this white launchscreen is not the default AIR one, and that my custom launchscreen is not taken into account?
Do you think the procedure I described above is correct? Thank you very much!