You can toggle your microphone on or off by clicking on the microphone icon before joining the Google Meet
You can toggle your camera on or off by clicking on the camera icon before joining the Google Meet
You can access the microphone and camera icons during a Google Meet by hovering your cursor near the bottom of your screen where the icons will pop up from the bottom of your screen.
Click the icons to turn your microphone or camera on or off.
CTRL + D will also toggle the mic on and off.