I am looking for a way to switch the app to portrait mode, so I can fit my ipad 9.7" into the rc clamps.
The video below shows it's possible. But nothing happens when I swipe left.

Is it an android-only feature?

The menu is there on both android and IOS. However, some features are not supported by the spark

Oh, I just realized that it is a support feature for the mavic, which has a camera that can be rotated.
It does not rotate the app. So ipad air and similar do not really belong in the compatibility list.
The rotating feature is secret 2 here: