https://wccftech.com/assassins-creed-valhalla-dynamic-4k-xsx/

Like the PS5 version, Assassin’s Creed Valhalla doesn’t run in native 4K resolution on the Xbox Series X.

Recently it was confirmed that Ubisoft’s latest installment in the series wouldn’t be running in native 4K on Sony’s console. Instead, the title uses dynamic resolution scaling up to 4K. Due to some confusing wording, some believed that on Xbox Series X, the title would be running in native 4K. As might have been expected, however, this isn’t the case.