Who I have the same questioned this topic

We just switched from Note 4 to S10+. Our voices during phone calls sound like we are covering the phone with a towel. These are brand new with cases and glass installed at Verizon. The microphone opening are not covered by plastic or anything else. People we call say they cannot hear us or cannot understand us. The primary function of this expensive phone is junk.

I see on the internet that there are a lot of people having similar challenges. Flushing caches and force stopping Bixby...

Good grief - it's a phone and needs to make a successful call!

Anyone else having this problem - how did you resolve it?