Here is another video showing the old prototype. The physics wheel slides, it does not rotate. But the mesh used for rendering does rotate (according to the movement speed). And as is visible at the beginning, the vehicle can remain stable if perpendicular to the slope.
Now I basically need to reproduce this in Godot.
This anisotropic friction thing is going to prove an interesting challenge (which is an euphemism for "I'm in a dead end").
The old implementation I made relied on PhysX providing the normal force applied to each contact point, which I need to compute friction. The more you press objects one against the other, the more friction forces prevent them to slide relatively to the other.
Sadly, #Jolt does not provide this information 😬