I am using Xamarin and there is no available option in the UI to specify "Requires full screen". I, therefore, had to follow @Michael Wang's answer with a slight modification. Here goes:
Open the info.plist file in a text editor and add the lines:
<key>UIRequiresFullScreen</key>
<true/>
I tried setting the value to "YES" but it didn't work, which was kind of expected.
In case you are wondering, I placed the above lines below the UISupportedInterfaceOrientations section
<key>UISupportedInterfaceOrientations~ipad</key>
<array>
<string>UIInterfaceOrientationPortrait</string>
<string>UIInterfaceOrientationPortraitUpsideDown</string>
</array>
Hope this helps someone. Credit to Michael.