Chosen Solution
I have a iPhone 8 and it was working all well but today I picked up my phone and saw these wierd black lines. I thought that they would be some moisture between the cables and will go off after some time. But it didn’t ! I had a little scratch in my screen but that was from a month ago and I dont think it relates with the black lines. It would be so nice if any of the geniuses could help me out with this issue.
To me it appears that air bubbles have formed in your display from what appears to be a crack in it. You can order a replacement kit from ifixit.com and fix it up yourself
You can try fixez.com for a replacement screen. They have good quality screens. I’m sure they will ship it. They are based in Las Vegas/Henderson Nevada