Hi Beres,
Thank you for posting, I am here to help you today. For Flickering screen and horizontal line, Test your screen if same inside UEFI of your Surface.
Turn off your Surface and wait 10 seconds.
Press and hold the volume up button on your Surface, and at the same time, press and release the power button . The logo screen will appear.
Continue to hold the volume up button . Release the button when the UEFI screen appears.
View the screen and see if the problem is still present. If the screen is working correctly within UEFI, the problem is likely with the software installed on the Surface. Proceed with the reinstall the display adapter and OEM panel driver section.
For more details you can check this article:
Troubleshooting options for a screen that flickers:
Troubleshooting options for a screen that has lines through it:
If the screen is not working correctly within UEFI, the problem is likely with the hardware. Proceed with submitting a service order.
Open the Surface App on your Surface device or you can download it from the Microsoft Store if you don't have one.
Click "Help and Support" and then click "Get Help".
Briefly describe your problem in the text box, such as "Lines appear on Surface screen", and then press Enter.
Click "Contact Support" at the bottom.
Select "Surface Studio" and click "Confirm".
You will see "Chat support" and "Phone support" options, please contact them during working hours, you will get one-to-one support services.
I hope you find this information helpful. Please let us know if you have any further questions If the answer is helpful, please click "Accept Answer".
Best regards,
Jansher