Thin green line on left side of iPhone 14 screen

Try a Forced Restart, but if it doesn't help, you have a hardware issue, which means a visit to the Apple Store Genius Bar for evaluation and service options.

Force Restart --> Force restart iPhone - Apple Support

Genius Bar Reservation --> Genius Bar Reservation and Apple Support Options - Apple

First, try a forced restart. If that doesn't work take it in to the Apple store to have it looked at.

• Press and quickly release the volume up button

• Press and quickly release the volume down button

• Press and hold the side button.

• When the Apple logo appears, release the button.

Force restart iPhone - Apple Support (IN)

Make an appointment at the Genius Bar to have it diagnosed.

Genius Bar Reservation and Apple Support Options - Apple