I do not know how to ask this question more formally. I was looking for state management in React while using Next.js, for example redux or react-query. I have seen a lot of comments that say something along the lines:

Be careful to NOT do that because the users of your application will share the same state

I do not fully understand what this means and how to actually implement something like this to grasp why and how is happening.

So is there a minimal example where you set a state management "the wrong way" and different users can access the state of other users ?