Yangyang: “I remember Comprehensive Mirror for Historians mentioned this in the Huanglong section's opening... ... A celestial being descended, commanding the Quiankun's boundless (universe) power. Assuming mortal form, they condensed the primordial essence, creating Pangu. Cleaving heaven and earth apart, they aligned the longitudes and latitudes, declared the four cardinal directions and Huanglong's history began, first separating the court and city.”
https://www.youtube.com/watch?v=xOn_aOXq1ZY&t=109s
“condensed” → “When water vapor in the air (often described as humidity) comes into contact with a colder surface, the water changes from a gas to a liquid and collects onto the cold surface.”
In my opinion, Pangu was the primordial (gaseous) substance of the universe<-Quiankun.
The celestial being condensed this gaseous substance into a liquid form called Pangu. It enables space-time travel between dimensions
I believe that Pangu is the liquid substance through which the Rover travels in the Opening Cinematics, and which enables space-time travel between dimensional planes.