2011 Subaru Outback - Infotainment issue

I have lines on screen when I put car in reverse

Just a guess but it sounds like static. There’s probably a poor connection to the backup camera at some point.

11 year old car, 11 years for corrosion to creep into connections and for electronics to fail.

If you mean you can’t see the backup-camera image clearly, you could try cleaning the lens.

If the screen looks normal the rest of the time, the problem is most likely the camera or its wiring.