I have created a customized my Sharepoint list form with PowerApps, and this is working great in the browser. I have the fields layed out in meaningful tabs, and I use rules to create meaningful behavior in accordance with the desired business logic.
All this is working great in the browser, but when I use the Sharepoint App for iOS or Android, the PowerApp form is NOT used. Instead the user sees the standard form with all the fields in one long row, and with no business rules applied.
The Sharepoint App should use the same form as when using the browser. Mobile first anyone? ;-)