Not seeing your Mute All button in your Teams Meeting? Click the Participants icon on the toolbar, then the ellipses, and you'll find it in the drop-down list!
Microsoft Update: December 10, 2020
New look when you join a meeting using the app : When you join a Teams meeting using the app, you'll be greeted with a new look to your audio and video settings. Select an audio setting on the right(1) to activate the Join now button (2)(Typically you will want to select the Don’t use audio option. Audio can then be turned on, as needed, once in the meeting). On the left, you'll see a setting to turn on background effects. Need to find a specific mic or camera? Under your video preview, select the gear to open device settings.