You can use a USB webcam or a document camera and still use your Mac's built-in webcam to show you speaking. This article shows how.
Important note: The AverMedia 300AF webcams(some of the oldest ones still in use in the district) are not compatible with the M1 Macbook Airs. However, this will work with just about any other USB-connected camera or document camera.
How to set up the 2nd camera in Zoom
With the webcam connected, start or join a meeting. Click on "share screen" and then click on "advanced" then select "Content from 2nd camera" and click "share".
Image description: a screenshot of the Zoom "Share screen" selection window. An arrow is pointing to the "Advanced" tab, which is selected. The option "Content from 2nd Camera" is highlighted as well.