Diagnosing laptop issue

Mods delete if needed.

Hey community, Laptop novice here. I need the best way possible to diagnose a rather expensive laptop I have.

It recently stopped outputting the display. Turns on fine. No screen. I have built gaming desktops in the past but laptops are fully distant to my comfort zone. I dont have any specialised tools or gadgets anymore and I'm unsure if I have the ability to fix. I dont need the laptop anymore, but to on-sell it I'd like to at least know what the issue is.

Any and all help appreciated :(

Gigabyte Aorus 15P 144hz display.