Funny you should mention that. I just tried to get rain working in AC using Proton. I sunk so many hours into it unsuccessfully that I decided to just buy ACC instead because it has rain built in.... After that experience it was very satisfying to select rain in the drop down and it just... rains.
EDIT: Automobilista2 has rain too. I was just angry at everything and ACC was my "throws hands up in exasperation" impulse purchase.
For me it was anyway. I think ge-proton has a lot to do with that though. There are tons of QOL patches in there.
I was having trouble remembering what the problems I had were but I'm pretty sure they were input device related. Also Trying to start multiplayer games with friends caused crashes sometimes.