Yes, I know it was. And yes I know there are a variety of world model numbers. Are you saying that only one specific one is having the problem? Which one? Or are you trying to claim there are different versions of iOS 14 for all those models?
And what diagnostics are your referring to? Are you saying that everyone in this thread went to Apple and ran diagnostics and said everything is fine? I've read the entire thread and I didn't see that.
As I said earlier I had a 7 Plus which I handed down and it encountered this issue. It was not during an update. The only microphone that worked was BT and the speakerphone capability was grayed out. It was a loose Audio IC. Ended up trading it in. It isn't too hard to do an internet search and you can find videos about this including demonstrations of reballing the chip and suggesting that 4 connections be done.
If your iPhone does not exhibit the same symptoms then it may be something else. If you have reported it you can wait until an update is released and see if it fixes it or try other remedies. But if no microphones are working and your speakerphone is grayed out it is almost certainly a loose Audio IC. And no software update can fix that.