Did the latest iOS or Zoom update break screen sharing when in split-screen mode?
This is related to iPadOS 14 and all apps that screen share will need to update and use a new SDK/API or Apple needs to ship a new update for one app to broadcast the content of another sandboxed app.
On iPadOS 14.0.1 only local recordings can record split screen multitasking, no apps I’ve tested can broadcast. We are evaluating if we use a video capture device or have a computer present while we wait for updates from our conference vendors (Microsoft, Zoom, etc...)
Here is an article about zoom screen mirroring for iPad:

https://support.zoom.us/hc/en-us/articles/201379235-Sharing-your-screen-iOS-with-the-Zoom-Desktop-Client