I’m unsure of your expectations - but consider the following...
Unlike PC and Mac computers, with which you are doubtless familiar, iPad doesn’t have the equivalent of an extended desktop - supporting content display across multiple displays.
iPad has Screen Mirroring - that reproduces what you can see on the iPad display - on an external TV or monitor. Screen Mirroring does exactly as its name implies; the iPad screen is reproduced on the external display, preserving both the content and aspect ratio of the iPad screen.
AirPlay extends capabilities of iPad - permitting display of playing media content (either download or streamed) to an external TV or monitor, at full resolution and aspect ratio of the source material, independently of the iPad screen. This capability, however, does not extend to other Apps.
In a touch-interface environment, an extended desktop contextually makes no logical sense; you’d not be able to interact with Apps displayed on an external screen. Screen Mirroring displays the iPad screen on an external display - but all interaction with the App is via the touch screen of the iPad.
I hope this information and insight is helpful in addressing your question - if only in promoting some additional thought.