Black background on iPhone 14 screen

Please try a force reset procedure as shown below:

• Press and quickly release the volume up button.
• Press and quickly release the volume down button.
• Press and hold the side button until you see the Apple logo

Force restart iPhone - Apple Support

If a force reset doesn't rectify this issue, then this is like a hardware issue in which you need to visit an Apple Store or Apple Authorized Service Provider for service.

Genius Bar Reservation and Apple Support Options - Apple

elain130 wrote:

Thank you for your help unfortunately it didn’t help ☹️

Then you will need service as I stated above.