Twinmotion can easily change the weather, but the rain effect seems to be a representation of the surface of the water. Also, depending on the angle of the vertical plane, they were undulated like the water surface. This is the limit of Twinmotion's expressive power.
However, it is good that water drops dripping on a near vertical surface were realistic as if they were on a real glass surface.
Twinmotion rain rendering test