iPhone 14 suddenly showing X-ray like images

Where are you seeing this?

If this is on the Lock Screen, you may have chosen a photo and then applied a black-and-white style to it.

Create a custom iPhone Lock Screen - Apple Support

There are also some accessibility features for vision that would change overall colors from normal.

Accessibility features for vision on iPhone - Apple Support

Please share a screenshot of what you’re seeing. I suspect you have accidentally activated features in Accessibility such as Invert Colors.