iOS 15
Change FaceTime audio settings on iPod touch
Turn off the sound
When you’re on a FaceTime call, tap the screen to show the FaceTime controls (if they aren’t visible), then tap to turn the sound off.
To turn the sound back on, tap the button again.
When your sound is turned off, your mic detects whether you’re speaking, and you’re notified that your mic is muted and that you can tap to unmute it.