Wow, thanks for sharing this. I was about to return my iPhone. Feeling so stupid now was testing microphone with all those protective covers on it.
My XR microphone worked for phonecalls and voice memos. But not for taking videos as there would be a lot of hiss and patchy underwater-like sound recording with silences and gaps.
After doing all the recommended suggestions including toggling of various sound options and even doing a reset that caused the loss of all my preset wifi passwords and customised settings, I finally solved the problem.
There is actually a 3rd microphone near the rear-facing camera that was covered by the rear phone protector. Cutting off a corner of it to unblock the microphone hole did the trick. All that unnecessary sweat wasted. Hopefully this helps for some of you.
I have a very similar problem. Sound in video sounds patchy and sort of like auto attenuated. Even without protective case, I have this problem. Speech memo app works just fine. What else could be the problem? Already restarted the phone...
iPhone XR - microphone issue ?