The rain was broken with SU5, before DX12. It’s still broken on both DX11 and 12. It’s a known bug. With lights off you won’t see the rain in the air.
It’s amazing that people are now championing features of a legacy weather system app that MSFS live weather already had and could do much better before. But I get it, this thread is about selling a product. Not about improving the core simulator. Because if they did that they would drive sales away from 3rd party devs like HiFi.