The premise of smart cities is their interconnectedness and the ability to track both the content and the connections of people within that city.
This is similar to the problem, that, for instance, TikTok poses on a micro level: that an adversarial actor can learn a lot about people, even if it cannot read their content. It's understanding the edges that connect different notes—that is to say, how often you, Mrs. Gallant, are communicating with someone else in your network. In addition, the ability to extract that data would allow an actor who can decrypt it, through quantum or more primitive measures, to then build a very comprehensive picture of your behaviour, Mrs. Gallant, and then potentially deploy misinformation and disinformation campaigns that are deliberately and intentionally targeted to your specific behaviour. That's in order, for instance, to influence your current behaviour, as well as to collect that data over many years to then influence your behaviour in the future.
That is the concern with TikTok. It's the ability to both influence the generation now and keep data on those individuals so that adversarial actors can attempt to influence their behaviour once they become voting populations.