Chiming in from another notebook model (ROG G703GX). After repasting, the computer ran for about 5 minutes, then abruptly blacked the screen, while still playing my music and at some point "screeched" and shut down abruptly. After turning it back on, it presented me with this exact issue. Green flickery lines everywhere, danger sign on device manager, etc. I forced a restart by forcefully shutting it down multiple times. 5/5 times the lines came back.
These lines ARE a defective GPU, 100%.
I still can't say for sure what it is/was, but I opened it back up, removed the heatsink and removed all the excess paste around the die that got on the little resistors/capacitors on the GPU chip (the green part) and put a (kapton, but any should do) tape all around the GPU die (on top of the capacitors) to isolate them further from the paste and also the aluminium heatsink that could maybe have touched them (or was so close that it conducted via thermal paste idk). After that I reassembled it, started it back up and all lines were completely gone. Even tested some Minecraft with heavy Shaders to stress the GPU and it's completely okay.
However, this could be coincidence, meaning that just the unscrewing of the screws around it could have positioned the board in such a way that it made contact again. I am writing this literally 15 minutes after doing said fix.
What I am sure, however, that is is an issue with the GPU die (cold solder, short due to conducting thermal paste, etc).
If you're reading this and see this happening with a laptop that you've never opened, sent it to warranty immediately.
Also, the above answer is kinda "have you tried to turn it off and on again?". It wouldn't make sense to be the screen, since the images clearly show the BIOS completely free from these lines, which makes sense, since the GPU drivers aren't loaded yet.
Furthermore, <insert brand> support are mostly useless, too. They ask you to do generic stuff and most of them don't even have an IT background or anything related. This has nothing to do with driver issues or a windows install, unless your preinstalled OS came with completely wrong drivers, which seems highly unlikely.
It is a hardware issue.