I think i found the answer: If world to screen to point is Vector3.Project … then Screen To World point must be Vecter2.Unproject
From @Deltakosh
var vector= BABYLON.Vector3.Unproject(
mousePosition,
engine.getRenderWidth(),
engine.getRenderHeight(),
BABYLON.Matrix.Identity(), scene.getViewMatrix(),
scene.getProjectionMatrix());
where mousePosition is the Vector2 with the screen X/Y coord you want to convert to world space
Right ???