BEPUphysics

how do i fixed the rotation or position for certain axis in bepu v2 like unity?

https://docs.unity3d.com/ScriptReferenc ... aints.html

You can zero out a row of the body's inverse inertia tensor to lock rotation around a body's local axes. There is no equivalent body-intrinsic position lock; you can do similar things with constraints like the LinearAxisServo or, more approximately, just by setting the appropriate component of the position and velocity to 0 every frame.