As ubisoft have said both run at 4k/60 (with no mention if that's native or upscaled) and this PR representative only refers to PS5, there is no indication that Xbox Series X isn't upcaled too. You should wait for your "my box is better" ammunition.
But the difference between PS5 and XSX is minor. PS4 had a 40% more powerful GPU which resulted in 900p vs 1080p. XSX is just 17% more powerful... it's less than half the difference there was between PS4 and Xbox One. It's going to be barely worth mentioning.
If Xbox One is 900p vs 1080p PS4. (31% less pixels)
PS5 will be at worst 1998p vs 2160p. (15% less pixels) (a.k.a 999p vs 1080p)
At that point who even cares?