It is a button prepared by the system. If you build the iPhone app on your iPad, it will always be displayed in the lower right corner. However, the number of buttons changes depending on the supportedInterfaceOrientationsFor setting of AppDelegate and the supportedInterfaceOrientations setting of the screen. There are not always two.

Thank you for providing the information! I look the tutorial. However, I'm hoping it will be fixed in the code and xcode settings, not the iPhone settings. But that's not the solution I was looking for. By the way, putting the app in the background and back to the foreground solves this problem and the screen shows the right number of buttons. What I want is to change to the right number of buttons without having to put them in the background.