You have encountered a significant limitation of iPad. Unfortunately, at present, what you are attempting to achieve isn’t possible.
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 the 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 video conferencing Apps such as Zoom.
Consider also that video conferencing Apps rely upon the microphone and speakers of the iPad. Whilst Screen Mirroring remains available, it contextually makes no logical sense given the technical limitation of the iPad camera and microphone that are necessary for video conferencing.
A further complication is audio. When using AirPlay, all audio is directed to the external monitor - whether or not it has sound capabilities. For a TV (or connected audio system) this isn’t an issue.
I hope this information and insight is helpful in addressing your many questions. I’m sorry that there isn’t a technical solution to what you are attempting to acheive.
