Hafiz629 Said:
"Muffled audio quality when recording videos on iPhone 12: This did not solve it :( but thank you again!"
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You are welcome.
Troubleshooting the Microphones:
Try this site: If the Microphones on your iPhone aren't Working - Apple Support. Note that there is more than one microphone on your iPhone. So, when recording, be certain you leave external headsets not plugged in.
Perhaps this is a Faulty Device?:
If the microphone is not working as intended then perhaps this is a faulty device? You have 14 days to return it. So, if it has been 14 days or less, then return it. If it has been more than 14 days, then have it serviced. You have a one-year, out-of-the-box, limited-warranty on this. So, contact Apple Support, seeing if they will return it or service it free of charge.
Contacting Apple Support:
Why the Wait:
Phone calls are taking a bit to go through at the moment, due to lots of calls. With the Coronavirus Pandemic, many are at home at the moment, with much time on their hands to contact Apple. So, just stay on the line, and you will get through :)