Zoom screen sharing not working on Ubuntu 24.04

I have two computers that are both running Ubuntu 24.04 with Zoom 6.4.13 (2309) installed from the .deb. On one computer I am able to share the screen, but on the other, I cannot for some unknown reason. When I select "share" at the bottom of the zoom meeting window, it opens up the "Select a window or application that you want to share dialog", but when I select what I want to share and hit the "share" button at the bottom, nothing happens. The same procedure on the other computer then opens up a second system dialog asking me what screen to share and then it shares the screen, but on this computer, nothing happens.

What is the problem and how might I go about diagnosing it?

Thanks,

David