It's not in official or nightly builds right now because it's still in development. The recent video you saw was for the Series S/X, which is also in the process of development and isn't quite perfect yet (IIRC MVG said it was a huge pain in the ass just getting it to run).
https://github.com/aliaspider/pcsx2/releases < You can grab the latest Retroarch Core binary from here if you want to, but IMO don't bother because it's definitely not a finished product.