My surface screen has a faded vertical line down the middle

Run the Surface Diagnostic Toolkit

Enter the BIOS and check if it's visible there-if yes, then it may be hardware related.

To access the repair guide for your Surface device:

Surface Service Guide Center

https://learn.microsoft.com/en-us/surface/service-guides/surface-service-guides

How to get service or repair for Surface

https://support.microsoft.com/en-us/surface/how-to-get-service-or-repair-for-surface-b06da716-0763-65b3-e2f2-116d9e30f877