I don't think we will really know before DF tell us. But yes, If PS5 is like 10-15% sub 4k reconstructed and Series X is native 4k then having similar reconstruct on Series would help, but I do think both are native 4k (it is near 4k on current gen if I'm not wrong).
Ubisoft producer confirmed yesterday that the Series X is not native 4K but is Dynamic 4K after all. GameReactor also said the same thing.
"I have a Series X behind my desk and the first time I booted the game on it I was super-impressed by the smoothness that 60fps brings to the most action-packed moments or just exploring the world. There will be shorter loading times and a good frame rate that make the game a lot more comfortable to play, as well as stuff like better draw distance, dynamic 4K and so on."
"On the Xbox Series X, Valhalla runs with a 4K resolution (it seems dynamic, as at times there was some notorious reduction in definition) and at 60 frames per second"