iPad

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 such as video conferencing.

Also consider that in a touch-UI environment, an extended desktop would make no sense; you would not be able to interact with Apps that were only visible on the external monitor.

iPad however can be used to extend the desktop of a PC or Mac computer - using applications such as Duet and Sidecar.

I hope this information and insight is helpful in addressing your question.