How to change the screen orientation on iPhone 12 Pro?

1. Swipe down from the top-right corner of your screen to open Control Center.
2. Tap the Portrait Orientation Lock button  to make sure that it's off.
3. Turn your iPhone sideways.

If the screen still doesn't rotate, try a different app — like Safari or Messages — which are known to work in landscape mode.

Swipe downwards from the top right corner to reveal the Control Centre, then tap the icon with the circular arrow & lock.

Turn the whole device to landscape or portrait.