I made another test that it is, in my opinion, remarkable.
In this state, if I connect a bluetooth headset, the calls work. The remote party can hear me.
So that is:
- Phone call: microphone does not work, captures something, but just noise
- Voice recorder: microphone works fine.
- Phone call with headset: remote party can hear correctly.
This basically rules out LTE or mobile connectivity issues, as Support has asked many vague questions about distance to towers or mobile operator.