iPhone XS display has faint white horizontal lines

It looks like a screen issue, but we can't diagnose it remotely.

Since your device is still covered by warranty, have it inspected at an Apple STore or Authorized Service Provider. After checking it out, they'll give you all the available options:--> Apple – Location Selector

Regards

Giulio

If it is a manufacturer's defect, it will be repaired or replaced for free.

As already stated, we can't judge, test, diagnose that kind of issue remotely, sorry.

Regards

Giulio