Front speaker issues on iPhone XR after iOS update

The volume of the front speaker became extremely low right after iOS 16 update. I updated the iOS on the iPhone XR last month AND yesterday night.

After I have successfully installed the new iOS, the volume of the front speaker became extremely low. I can still hear audio output from the speaker but only when I’m in a very quiet place. Yesterday, I installed the latest version of iOS (16.2). The situation became more severe. The speaker is still workable but the volume became much lower.

I have tried many ways to try to fix the issue.

1. Update iOS to the latest version
2. Clean the front speaker
3. Update all applications from App Store
4. Reset all settings to default
5. Turn off silent mode using the switch on the side
6. Keep pressing side volume up button when my ear is close to the speaker as well as when it is not (the buttons are workable as the iPhone shows the volume up screen)
7. Restart the iPhone
8. Remove screen protector
9. Turn Bluetooth off

Remark 1: There is no problem when I use the external speakers on the bottom and earphones.

Remark 2: The volume is low in calls and third party apps from App Store. So it is not likely a third party app issue.

Remark 3: No jailbreak.

Remark 4: It was good before update and the problem occurred right after iOS update. When the phone restarted from installation, the issue appeared. So I don’t think it is a hardware issue.

Does anyone knows what is going on and how to fix the issue? Thanks.