Hi,
As you can see on the capture below, the App object is not displayed in the intellisense when typing the keyword "App" in any control property of the PowerApps web editor (while other similar objects like Compass, Acceleration, ... are shown in the intellisense):

Probably a bug... Thought I'd report it...
Note: properties of the App object can still be accessed through the intellisense if you just type the dot "." after "App"... 🙂
Emmanuel