How to change screen display from vertical to horizontal on iPhone 12 max

Make sure that your iPhone does not have screen lock on. To check, I think you have to (with newer models) swipe from the top right side of the iPhone display or the very bottom of the display, and it will open a screen that looks like this: it’s called the Control Center. If the circled icon is white & red, then it means screen lock is on. Press the icon again to turn off. Horizontal view will only work with specific apps, such as Safari. once you turn it off ( or not if it’s already off ) just turn your iPhone horizontal (either side will work). Hope this helps!