Hi PradyGee, I think I made progress but I'm not sure you're going to like it unfortunately...
From my understanding it is something that is decided by the website's javascript (or potentially the OS), but not by the browser.
In your detailed video, we can see the website zoom.us offers to pick which camera, it looks very much like a control Zoom designed, it matches their other buttons.
I put together a test page with simple Javascript to display the video feed from the camera, and with a camera selector. Please have a look at this page:
https://jeanetienne.net/orion/camera.html
I am still curious about your mention of your Lenovo tablet offering this option. Where in the settings does your lenovo tablet let you pick the camera? In the browser settings (which browser?), or in the OS settings?
Thank you for your help in troubleshooting this issue!