I have experienced similar issues as well. I think it needs to be fixed via a software update.
The WhatsApp call using loudspeaker picks up a lot of background noise, and when I speak, my voice is not heard properly or is muffled very bad. Needs an update immediately to fix this.
Have you changed your settings to only use your mobile provider and not use WhatsApp to make calls?
Have you tried recording your own voice or conversation using the installed Voice Recorder to check the quality of the microphone? (If you don't have that app, download it from the Galaxy Store.)
I'm having the same exact issue. It's not just WhatsApp, I tried it with Messenger, Google Duo. Both callers were using a Note 20 Ultra. It's really disappointing to have this issue with a $1,300 phone.
Hi I have the same issue, just as long I am using third party software e.g Whatsapp for calls, it will have this issue. It was not as bad with Viber but it was terrible with WhatsApp. I have contacted Samsung and their only advice is to do a soft reset and if it does not work, do a hard reset.