The difference here is that the PS4 Pro verison of the game never manages to hit 4K while the Xbox One X version can reach this target. This was confirmed in an analyze by VG Tech.
Even if we compare the lowest point of the resolution, the PS4 Pro version can hit 960×2160 on the low end and 2640×2160 on the high-end of the resolution, compared to the Xbox One X, which has a resolution ranging from 1920×2160 to 3840×2160, and it is already a massive leap while maintaining a steady frame rate.
Call of Duty: WWII is undoubtedly best played on the Xbox One X even if you own a PS4 Pro. The controller was already well suited for shooters but the release of the Xbox One X has made it the definitive console version.