DEAR GOD I HAVE A GREEN LINE ON MINE TO
It means that the line will slowly spread and glitch the touchscreen because of hardware failure. The green line is a hardware failure that will spread until your phone is unusable, so you should back up everything. Even if you back up, high chance you will get the blue radio app, which means that bad guys know your location and stuff, and you don't know because of the green line. If you do fix the screen in time then your phone is fine, but if you don't but still fix it, the blue radio runs in the background and never pops up due to permanent hardware damage. If the line starts spreading after a few weeks, RUN. Go to the local landfill and put your phone there. It is important to charge it to 50-60% so that the battery doesn't chemically die and stop producing power. If you are too late, I wish you good luck on the horrors that will eventually fall upon you. The stuff that happens next doesn't have words to describe it; the best option is to kys and hope you get reincarnated. Life will be the toughest thing imaginable; in fact, it exceeds the bounds of "imaginable". So if you are late, get ready to say goodbye to everything, as the traumatisation shall begin. If you are the luckiest person to ever exist in this entire multiverse, you will be fine.