UPDATE: FLICKER IS SOLVED!
So to update you on my findings this morning about our iPad Air 4 (2020):
The severe screen flicker and video noise WAS indeed produced using the Camera app in front-camera mode.
I connected with AppleCare chat yesterday, and the tech first ensured that I had the latest iPadOS update, which I did. Then she told me to reset Network Settings as a way to remedy the video flicker. Instead, frustrated and assuming this reset would be useless (asking myself, How are network settings related to the camera!?), I ended the chat, drove to the local Bestbuy, they confirmed the screen flicker, and made me another appt. to have the iPad sent in for repair/replacement.
Well, today, on a whim, I decided to Reset Network Settings. After a lot of testing time, to my surprise and delight, the front camera screen flicker has now completely disappeared from the 3 apps I saw it on before: Facetime, Camera and Photo Booth. I have NOT tested the camera on Skype, Zoom or any other apps.
So here's this from Apple support:
"Reset your Network Settings.
Go to Settings > General > Reset > Reset Network Settings.
This also resets Wi-Fi networks and passwords, cellular settings, and VPN and APN settings that you've used before."
Good luck all - I hope this helps!