Does the Oculus Quest 2 have a built-in mic?
The answer is yes, and the microphone is located alongside the speaker. The benefit of having a built-in mic is so that the user doesn't have to connect any additional devices.

The sound and mic are all in one place without having other wired components attached.

However, the 3mm audio jack on the other side of the headset is output only. So there is no input function for an external mic.
Oculus Quest 2 Mic Sound Quality
The mic quality does quite well for VR chat and games.
The user also has the option to mute audio input inside VR.
However, for higher fidelity voice recording for content creation, we recommend attaching a dedicated microphone.
Check out the Antlion Wireless Modmic
Benefits Of An External Condensed Mic For VR Use
- Higher quality audio input for VR game play, VRChat or VR related content creation
- Mic follows you wherever you go in the VR space instead of using a stationary boom mic in your room
- Uni mode is preferred to block out background noises
How To Switch Oculus Quest Mic Input ?
1. Go to your computer's sound setting and switch the default input device to the microphone
2. Go to Oculus Device setting, and change default mic to whatever you're using to replace the built in Oculus Quest mic