Oh it has to be the real Werner. It’s such a perfect cameo.

Edit:

While the W.E.R.N.E.R voice does sound like Herzog, the director opted not to join the franchise… Herzog was approached to voice the role, but “respectfully declined.” Instead, the A.I. was voiced by Ross Marquand, who also voiced Ultron in the animated show’s first season and played Red Skull in Avengers: Endgame.

https://comicbook.com/marvel/news/does-werner-herzog-really-cameo-in-marvels-what-if-season-2/