Try getting into safe Mode with minimal controllers activated, No network, no graphics, nothing, minimal Windows Safe Boot, then try to shut it down, if it does shut down we can know for sure that some controller, driver or process is behind it instead of some BIOS Hardware related setting.
After doing this try again in safe mode with network capabilities, and go adding more controllers as you go, if you can shut down at every single safe mode then do a selective startup with only Windows Process and see if you can shut your PC Down, this way you'll at least know if the culprit is some Windows process, but if you can shut it down then its some external process like a driver or some kind of software unrelated to any controller that will only run in a non-selective startup environment.
Damn, didn't knew you could buy Melatonin, though it was illegal for some reason lol, going to look into it, doesn't it make you an addict tho? in the sense it might be harder later to get sleep without it.
Just reinstalled windows and I'm still having the same problem.
I think it has to do with the bios update. Can I hold Asus accountable for this??