Hey there, and welcome to Apple Support Communities, awaters11!
From our understanding, when recording videos using your iPhone, the audio sounds muffled. We’d be happy to help out!
You’ve done some great steps so far by using the article specifically for microphone issues. Since you mentioned that you tried using this on other apps and it doesn’t occur, did you try making a FaceTime call and use both the front and back cameras to see if the same thing occurs?
Did you follow these steps in the article that you posted?
If the microphones on your iPhone aren't working
Clear the microphones
- Remove any screen protectors, films, or cases from your iPhone.
- Clear any debris from the openings of your iPhone.
When recording or making a FaceTime call to someone else, the microphone in use will depend on the camera that is active.
If you have done that troubleshooting, we’d recommend that you Contact Apple Support.
Cheers!