Right so Myself and a relative both have pixel 7s, one standard, one pro which is mine.
The last week or so we have been having issues where the call cuts out and no one can hear us on the other line. I just had to get an old fliphone out to talk to someone important without any issues. I thought it was just my phone but when my other relative's phone starting having issues I got suspicious. It does not seem likely to be a hardware fault.
Calls through signal are perfectly fine. So it is not a mic issue or a hardware fault. Another relative on the same network different phone not a pixel works fine.
This seems to be a Graphene OS issue as hardware is ruled out, network provider is ruled out and so on.