The goal was to launch the app when the public version of iOS 13 is released -- that is Sep 19, 2019.
It is a tight one. I submitted the app to Apple review 7 days before that "dateline". And it took a long 7 days to review, with 2 rejections, because the APP ICON looks too much like Apple's iPhone camera lens!
It is a lesson learnt, and I comply and change the app icon design.
It was approved and is available on Sep 19 :)