Sharing my screen kills my outgoing sound

I am trying to use Jitsi to work round a problem in BridgeBase Online’s voice feature. What I need to do is to be able to share my screen and talk to the other participants (the people attending a bridge class) at the same time. What appears to happen is that sharing my screen means that, while I can still hear others, they cannot hear me. As soon as I switch off the screen sharing, the problem disappears, everybody can hear me again. I’m using via Firefox 88.0 64-bit under Linux Mint 20.4. Can anybody tell me if I am missing a setting somewhere which would enable me to talk over the screen share? Thanks!

Are you using screen share and webcam at the same point?
Or just when screen sharing?

Have you seen the same behavior on Google Chrome?

I’m starting off with the webcam, and then I want to suspend/kill the webcam and share my screen. I can try it again with the webcam off. It’s also been suggested to me that I try Chrome, I don’t have that installed but I guess I can do so (I try to avoid Google), I’ll try Chromium first. It may take me a day or two to find time to do this testing, I will report back once I’ve done it. Thanks for the hint!