Samsung Galaxy Z Flip 3

I had the same problem - it was a screen failure and the phone had to be replaced.  If your's is still under warranty, it should be free.

changing your wallpaper doesnt do anything correct? you see the same thing no matter what the background color is?

any way you can take a pic and post it in here?

avoid posting any personal info with the pic..just the screen itself with nothing personal on it.