How do I disable the Cities of Tomorrow Expansion for SimCity?

From what I know, sadly, there is not a way to disable any content in the game. Since what you have is the Complete Edition, there is no way to partially uninstall either. Yet, my experience was different – if I do not want futuristic features, simply avoiding Omega Co. plants or the Academies will do the trick, but seems like it is not in your case. I suggest maybe double check whether you accidentally plopped any futuristic building; if not, then I cannot be of much help here.

Have a nice session.