AFAIK rain shorts doesn't exist. Rain chaps OTOH do:https://www.rosebikes.se/artikel/rai...ion/aid:288722
I have a pair myself that I'm reasonably happy with.
There's a strap that occasionally gets hung up on the nose of the saddle, but that's about it.
Acting as a wind break, they provide a surprising amount of extra insulation, and I sometimes use them for the warmth only. Being entirely open at the rear, ventilation is fine.

I have some weird Adidas 3/4 length baggy trousers which are quite waterproof. IMO they don't work that well for the same reason full length rain trousers rarely work well for dedicated riding - you get clammy/wet from the inside instead.