If the generation was successful, physics data has been written to this MeshGenerationResult.MeshCollider.
Check MeshGenerationResult.Status to determine if the generation was successful. MeshGenerationResult.MeshCollider may be null if a null MeshGenerationResult.MeshCollider was provided to XRMeshSubsystem.GenerateMeshAsync.
Additional resources: XRMeshSubsystem.GenerateMeshAsync