Alright so a bit of an update for me. Instead of clicking direct download on https://acstuff.ru/app/ I instead tried Mickeymouze5 suggestion of using google drive. After I downloaded the zip file I extracted it my Assetto Corsa install directory.
For you the address should be the drive you installed it to and then "SteamLibrary\SteamApps\common\assettocorsa"
After I extracted it I navigated to the folder itself clicked on the content manager.exe and it opened up just fine.
Hopefully this fixes your issue as well.