Maybe it's obvious for you guys but I scratched my head for a while because the folder didn't show up in the files app.
I actually needed to store something in the folder.
you could achieve this by
- saving some files into your document directory of the app
- move something from iCloud Drive to your app (in the move dialog the folder will show up). As soon as there are no files in your folder anymore, it's gonna disappear from the "on my iPad tab".