Run the check
Record speech locally and inspect both playback channels with headphones.
Check whether the source device reports mono or stereo input.
Compare the recording application's channel mapping with another recorder.
Read the result
Speech on one file channel does not mean the physical microphone is broken.
Limits and next step
The browser cannot inspect every application's export configuration.
Repeat the check after changing one setting or connection. Keep a record of what changed before deciding whether the device needs service.