When the Host and/or current Presenter has turned off Push-to-Talk as the session audio, the talk button is removed from the taskbar.
And, session attendees will have a solid gray microphone to the right of their name, unless dialing into audio using a telephone.
CONTROLLED BY HOST OR CURRENT PRESENTER
The Host and/or current Presenter can "mute" any attendee's microphone by clicking the gray microphone and choosing the option, "Deny This Microphone".
Or, the microphones for all attendees may be "muted" with just a click via Attendees Menu > "Disable All Attendee Mics". When this is selected all microphones are disable except for the Host and/or current Presenters.
Microphones disabled by the Host and/or current Presenter are denoted with three red dots to the right of the microphone icon.
To enable them again for all attendee choose Attendees Menu > "Enable All Attendee Mics".
Or, to allow for one attendee individually click the attendee's microphone and choose, "Allow This Microphone".
CONTROLLED BY SESSION ATTENDEE
Session attendees may individually mute their microphones by clicking on the gray microphone icon and choosing, "Mute My Microphone".
When muted by an individual attendee, the microphone icon is hollow with a red line through it.
The attendee can unmute by clicking the microphone and choosing, "Share My Microphone".