From Google:
The Pixel team paused the December software update to Pixel 6 and Pixel 6 Pro devices after some users reported calls were dropping or disconnecting. We have now identified a fix that will roll out in a software update by late January. This update will also include all the fixes and improvements that were originally planned in December.
If you received the December software update on Pixel 6 or Pixel 6 Pro and are still experiencing mobile connectivity issues, you can revert to the previous software version using the Android Flash Tool (flash.android.com) and performing a factory reset. Please back up your phone before restoring to the previous software version. If you are not experiencing mobile connectivity issues, no action is required. We sincerely apologize for the inconvenience and appreciate your patience as we roll out the fix.
It's all very disappointing. More so for people who put down their hard earned money on the 6 and (especially) 6 Pro, at least we at 'All About' have a loan device from PR. When the update does finally, finally arrive, almost two months late, will Google have fixed the lack of Super Res Zoom on the 6 Pro? Will they have fixed the muddled stereo from the speakers? Somehow I'm not optimistic at this point - Google never seems to allocate enough of its manpower to the software in its own phones, which is why it takes many months every single year before a Pixel device is properly stable and useful.
Watch this space.
PS. See also my full review of the Pixel 6 Pro.