Green Thin line on the screen

There's a small chance reseating the display cable could help, but frankly I'd be getting ready to replace the screen if I were you. They still seem to be somewhat expensive, so you'll have to decide for yourself if it's annoying enough to justify the cost and effort. The line isn't going to go away and it may or may not get worse over time.

Here's a video showing how to remove the screen; you could follow it up to the point of disconnecting the screen and just try unplugging it and reconnecting it to see if that does anything. I'm not optimistic, but it's really about the only thing you can do outside of just flat out replacing the whole screen. The phone he's working on is much worse off than yours, but the steps are all the same.

BENT AND CRACKED! ASUS ROG PHONE 5s Screen Replacement

I didn't do an extensive search for parts, but here's one of the first ones that came up for me. I usually check Amazon, eBay and AliExpress first, but it may show up on phone parts websites as well.

Amazon.com: Mobile Displays AMOLED LCD Screen for Asus ROG Phone 5s ZS676KS with Digitizer Full Assembly : Cell Phones & Accessories