iPhone 11 screen issue or just a manufacturing fault?

Hey,

About 4 days ago, while I was recording my lessons with the voice note app, I noticed something.

When I leave the VN app on-screen for a couple of seconds, and then go into the home screen you can notice a shadow on the screen. Then, after 10-20 secs, it disappears.

As the Apple Stores in my city are closed rn, I contacted an Apple authorised service center and they said it was an iPhone 11 screen issue, but none of my friends who own an iPhone 11 face this issue.

I've inserted 2 pictures where you can see a bit what I'm talking about.

Can someone help me?