During Google Meet call, other people can hear whatever I can from my computer without me sharing my screen. It can be Youtube, FB video from Chrome or song I play on the Spotify app, whatever kind of sound I play. How can I fix this, I'm using Ubuntu 20.04.
For more details, I'm using a headset with only 1 input jack for both sound and mic. I connect this headset through a cable looks like below. It has 2 jacks on 1 side which connect to my PC for sound and mic. The other side would connect to the input jack of the headset. 

pavucontrol, at "Recording" tab, check what is the input source for Google Meet when you have it open. You should be able to change input to microphone. – pLumo Nov 22 '21 at 15:35pavucontrolis not an "external" app but a more sophisticated sound setting program compared to the default one where you can change that. – pLumo Nov 23 '21 at 14:37