I have been playing with both sized iPads, and black bars can be found on both sizes for almost all non-Apple apps. There are two kinds of black bars: 1) Rounded corner black bars: This is similar to the iPhone X situation, before apps are updated to accommodate the extra spaces extended by the rounded corners. This affects both the 11" model and 12.9" model. 2) Aspect ratio black bars: This only happens on 11", and it is far worse and far more notifiable than the "Rounded corner black bars". If an app is not coded to dynamically adapt to aspect ratio, you'll see horrifyingly large black bars especially in landscape mode. It's almost like seeing an iPad mini sized app, inside an 11" screen. Populars apps such as Facebook and Netflix are affected by this.