Hi there and welcome
Can you do the following please
Shut down your Mac.Locate the following keys on the keyboard: Command (⌘), Option, P, and R. Turn on your Mac.Press and hold the Command-Option-P-R keys immediately after you hear the startup sound.Hold these keys until the computer restarts and you hear the startup sound for a second time.Release the keys.
Then tell me if it resolves the lines and flickering please
Power off the mac
Then start the Mac and hold down the Command and R keys at startup.
Hold these keys until the Apple logo appears. After your computer finishes starting up, you should see a desktop with an OS X menu bar and an OS X Utilities window
choose Disk Utility from the Utilities window, or from the Installer menu if you're started from an installation disc.
Click the First Aid tab.
Click the disclosure triangle to the left of the hard drive icon to display the names of your hard disk volumes and partitions.
Select your Startup Disk (usually named "Macintosh HD").
Click Repair. Disk Utility checks and repairs the disk.
Let this complete and when it has, tell me if you still have the problem please.
It is the LCD panel that has faulted. The controller is not communicating correctly with the Segments on the screen and this is why it flickers and gives the lines
I am really sorry about this and you are going to have to return the mac to have the panel replaced. It will be covered by the warranty if this has not expired, and the replacement will be done at no cost to you.
I am really sorry about this, and if you have problems, or would like any additional information or assistance, please do not hesitate to let me know.
And if you can take a second to rate my service by clicking one of the stars at the top of the page, then submit, that would be greatly appreciated.
yes, as the issue is with the actual screen (the physical part of it) so you will not see the issue in a screen shot
If you would like any additional information or assistance, please do not hesitate to let me know.
I zoomed in all the way and see none of this at all.
Send it to another device, eg: or phone and view the screenshot there.
As the lines are only on your screen, they do not appear here
It is an issue with the actual screen, 100% as the screen print is perfect here
Let me know if you need anything else please
and please remember the service rating