I've been wishing for this so much and after a lot of searching, ı finally figured out a way to play as carla in ada's campaign.
Thanks to this mod, it's possible to do so:
I tried to download the mod through a chinese site but it didnt work out, the download got interrupted for no real reason. After finding the links above however, ı've managed to download it.
I managed to download it by copying the download link ( which didnt open when ı clicked on it. ) and pasting it to another tab and opening it there.
There are 2 versions, one with gloves and one without gloves.
I tried both and they work well in campaign with cutscene support. I always wanted to play as carla in ada's campaign and now ı can do it after wishing for it so long.