Hi there zinah214!
Thank you for posting in Apple Communities. Congratulations on your new iPhone 12 Pro. It sounds like you are experiencing poor audio when you are using video apps. We can give you some tips that can help you remedy this issue.
To start, does occur when you are making phone calls or if you record your voice using the Voice Memos app? If not, what about when recording a video of yourself in the Camera app? There are multiple mics on the iPhone and checking using different apps helps isolate which mic is having trouble.
Does the issue persist if you are using headphones? Are you using a case on your iPhone? Remove it, and test to see if the issue persists.
Sometimes, Voice over LTE (VoLTE) can cause static or other sound issues. Check to see if you have Voice over LTE turned on:
Go to Settings > Cellular > Cellular Data Options. Look next to Enable LTE, if it says "Voice & Data", then VoLTE is turned on.
If you have it turned on, turn it off, then test to see if the audio issue still occurs. To turn off VoLTE, go to Settings > Cellular > Cellular Data Options > Enable LTE and tap Data Only.
Does the issue persist? If not, you will need to speak with your carrier concerning your wireless network.
If it does not, reach out to our support Advisors here: Get Support
We hope this helps.
Cheers!