This video is faked. Or rather it is showing an app which pretends to be Task Manager. Further done in the comments of the tweet it is demonstrated that this is fake.
More like: rendering Doom output as pixels in the task manager for hundreds of CPU cores. They didn't massively parallelize Doom itself, but just the pixel drawing.
Oh thank God for people like you. Correcting everyone all the time always no matter what. So brave.
I am always glad when someone calls out nonsense that wastes people's time. Even if this wasn't fake, the headline says something completely different than what it actually is. It isn't nitpicking to point out a lie.