Chosen Solution
I have a issue with a iPhone X, the camera app on the iPhone is flickering, and it does only happen indoor, outdoor the camera is fantastic and no problem at all. I uploaded a video of the issue i am facing here: https://streamable.com/oi5rg0 I tried hard reset, and changing framerate settings of the camera application inside settings, but none of the methods worked out for me. The issue is the same for the front camera, and the rear camera. The phone is running iOS 13.7 .
Were you near any LED lights by chance? Cheap LED lights can cause a flickering effect which can be picked up by cameras.
The problem is the iPhone x camera is 4 years old now the xr has a more advanced camera a12 bionic chip has better processing for camera and video images than the a11 on the iPhone x. You will find you get no flickering indoors on the xr recording videos and you get a clearer looking photos.