I bought a Fairphone 3+ less than two weeks ago. After setup I got this software-update and installed it.
The same day I tried videocalling with Whatsapp/Signal and ran immediately into the issues mentioned: The caller couldn’t hear me. Audio-calling other than normal phone gave the same problems when I tried to use the speaker.
I made a ticket but no answer yet.
In the meantime I flashed LineageOS 17.1. It was pretty easy and it solved problems I had with the official ROM. Normal calling is very clear, video calling with different apps are problem-free.
I hope the official ROM solves the issues but right now I’m happy with how the phone works.