I recently got an iPhone 13 and I noticed that it has a white line on the bottom when I want to change my wallpaper in dark mode. Is that a glitch or an hardware issue?

bernardino289,

Do you only notice this when dark mode is enabled on your device? Is this when attempting to change your wallpaper? Have you tried restarting your iPhone since noticing this behavior?

Restart your iPhone - Apple Support

How to restart your iPhone X, 11, 12, or 13

1. Press and hold either volume button and the side button until the power-off slider appears.

2. Drag the slider, then wait 30 seconds for your device to turn off. If your device is frozen or unresponsive, force restart your device.

3. To turn your device back on, press and hold the side button (on the right side of your iPhone) until you see the Apple logo.

Regards.

Thanks for giving that a try bernardino289,

Upon further examination, it looks like you may be experiencing image persistence. While this can be expected on some displays, the following resource that provides information about the behavior, also offers steps to minimize the effect.

Avoiding image persistence on Apple LCD displays

The first section of the resource, provides information about the behavior:

With some Apple LCD displays, if you leave an unchanging image (like a login screen or the same desktop picture) on the screen for a long period of time, you may see a faint remnant of the image even after a new image has replaced it. This is called "persistence". 

You can prevent image persistence, by shortening the Auto-Lock interval in Settings > Display & Brightness, which will also turn off your iPhone's backlight, which may prolong the useful life of the display.

Further down, you'll find steps that most often provide a solution to occurrences of image persistence:

In the rare event that an image does become persistent, you can usually get rid of it by following these steps:

1: Temporarily set the Auto-Lock setting to 'Never'.

2: Display an all-white pattern across the entire display for the same amount of time that the persistent image had been displayed on the screen. To do this: 

a: Create an all-white screen in a graphics application such as Photoshop, and save it as a JPEG file.

b: Use this as the image displayed on the Lock Screen and Home Screen.

c: Turn the display brightness down (but not off) to preserve backlight bulb life.

3: Verify that the persistent image is gone.

4: If necessary, repeat the process until the persistent image is gone.

5: Revert your Auto-Lock settings to a short interval

If you need more help after taking the information from this page into consideration, and completing the recommended steps, the best path forward will be to contact Apple Support.

We hope this helps!