"Join with Audio on Computer" greyed out and not accessible on Chromium/Raspberry pi 4

[UlrichFlamm]

Both in the browser and with Zoom PWA, the option to join audio with computer ist not available. The font in the button is greyed out and the button is not clickable. Video works well. The same problem is described here: https://raspberrypi.stackexchange.com/questions/130535/not-able-to-select-join-by-computer-audio-in-...

All the permissions are set to allow both the use of camera and microphone.

With other services like MS teams everything works fine.

I am using a freshly installed raspberry pi OS with chromium browser on a raspberry pi 4 (4GB) with USB webcam incl. microphone.

Thanks in advance for any help!