Accessibility: cannot use arrow keys to navigate web pages in VoiceOver when sharing screen in Zoom

I had a very disappointing experience when giving a presentation in Zoom today on web page accessibility. When I'm using Zoom, the arrow keys no longer work to navigate web pages in VoiceOver. There's no feedback; pressing the key just doesn't work. The exact same steps work fine when I'm not also running Zoom.

As a result, I wasn't actually able to show the people on the call how to navigate within a web page in VoiceOver, which was the whole point of my presentation.

Is this a bug, or something I've overlooked in the settings?

Steps to reproduce:

1. On MacOS, enable VoiceOver.
2. Open Safari. Go to any web page.
3. Enter the web content area. Use the up and down arrows to navigate through elements in the page.
   • Expected: pressing the up and down arrows navigates between VoiceOver-accessible elements in the page
   • Actual: as expected
4. Start Zoom.
5. Switch back to Safari.
6. Enter the web content area (if needed). Use the up and down arrows to navigate through elements in the page.
   • Expected: pressing the up and down arrows navigates between VoiceOver-accessible elements in the page
   • Actual: pressing the up and down arrows does nothing. There's no feedback in VoiceOver indicating that there's a problem. 
7. Quit Zoom
8. Switch back to Safari
9. Enter the web content area (if needed). Use the up and down arrows to navigate through elements in the page.
   
   • Expected: pressing the up and down arrows navigates between VoiceOver-accessible elements in the page
   • Actual: as expected