Technical issues with IOS 14.1 update

The Audio IC on your logic board has come loose. You can click on the Contact Support link at the top right of this page and start the service process, an out-of-warranty replacement phone will cost you $319 (Apple does not due piece-by-piece repair. If you can find a reputable 3rd party repair shop in your area that can do micro-soldering they should be able to repair it for about $145 USD. If you go that route Apple may refuse service on this iPhone in the future.

Most likely that is a symptom of a problem you already had that the update revealed. Can you use the speakerphone on calls or is it greyed out?

Same thing happened to me. I am aware of the Audio IC chip on the logic board but I had no issues making phone calls until iOS 14.1 was released. I'm waiting on Apple to release another update to fix this.

see this support article

If the microphones on your iPhone aren't working - Apple Support