We don’t have a mute microphone option once you’ve joined a session. But you can choose to Join without voice when loading into a session if you are coming in on a second device or do not want to hear/be heard.
If you can hear echo or feedback during the session, that suggests the other user is not using headphones. Ask them to plug some headphones in and that should improve the quality. If voice is breaking up, then that is likely due to one of your internet connections so please follow these steps.
If you are struggling with background noise then the quickest and easiest fix is to ensure all participants are using headphones with a built in microphone.
If there are users who are participating in the same session and are working from the same physical room, it would also help for them to sit far away from each other.