Hi @daliborvasic
Did you try using the phone in safe mode to prove that it isn't a software issue?
@daliborvasic
Bit confused.
Do you mean that there are now two phones with the same problem, yours and your son's?
There are 3 microphones in the phone.
On the bottom edge, there's a microphone next to the USB-C port and speaker. There's also a microphone located on the top edge, near the IR blaster and secondary speaker and a third microphone is situated on the rear panel, below the ultra-wide camera, between the main and macro cameras.
So whilst you may have problems when using the phone on a call in normal mode, you shouldn't have problems when using it in loudspeaker mode for example.
It is unusual for all 3 to fail at the same time unless the phone has been dropped, gotten wet or perhaps a system update had been done that didn't quite work.
If it also doesn't work in safe mode, the only thing that I can suggest is that you backup the phone to the cloud or a PC and then perform a factory restore on the phone, to reset it back to factory default condition. Then once that's done, test if it works OK.
Note: If there's a Google account associated with the phone, you will need to remember the account's user ID and password to setup the phone again after the restore has been done otherwise you will be locked out of the phone as the FRP lock has been enabled by the restore.
If it does work after a factory restore, restore the phone to what it was before using the backup you made earlier and test it again and check.
If it still didn't work after a factory restore then it's a hardware problem. Most likely a faulty mainboard
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