Ouch, hate it when that happens. Yeah, unfortunately there are four ribbon cables connecting the display to the motherboard, and it seems pretty definite that you've damaged one of them. If you open up the case and take the keyboard off, you can see those four black ribbon cables as shown in the [guide|144226|Microsoft Surface Laptop 3 15" Screen Replacement guide|new_window=true].
[image|2829388]
The bad news here is that the display is like the ones on the MacBook Air; if there's any damage of any kind, the only solution is replacing the entire display assembly. The following comment from the [guide|127277|Microsoft Surface Laptop 3 (15-inch) Teardown|new_window=true] is particularly relevant here.
[quote]These cables aren't modular, so if you cut one, you'll be pulling a MacBook Pro and replacing the entire display.[/quote]
Wish I had better news, but this is my best bet on a diagnosis.