This is how you activate the microphone in the game start screen
Online Mic Test Tool – https://www.onlinemictest.com/
This tool may help you know if the microphone is actually working. You have to see the waveform in the box as you speak.
Troubleshooting guide to fix microphone issues
A console device like Quest is supposed to be easy to use. But microphone access is an exception, probably because of the privacy issue.
1. If, by accident, you click deny on the start screen, it won’t ask you for permission again. You have to clear site permissions.
2. You may have your microphone disabled in the quick menu.
3. It could be the app permission issue.