Ok the restitution demo is fix now.
notice that the restitution demo does no uses the body material , instead it use the user data in the collision shape.
this makes it more easier to use newton with unilateral materials like many physic commercial physics libraries do.
The material graph is much more powerful but it but it is a legacy that use the body, many one day I will change the so that is use he collision shape instead,
but for now it is what it is.
Not the restitution and the buoyancy should be working fine.
I am working on the Vehicle now. and after that I will make a special 3DOF joint for ragdolls.