The way to keep it simple is to have a single state object, which is the one place where state is organized and accessed.

The way to make it scale is architecture. Architecture is a fancy word that means a repeatable pattern of instances where each instance of a thing represents a predefined structure. Those predefined structures can then optionally scale independently of the parent structure with an internal architecture, but the utility of the structure’s definitions matter more.

Boom, that’s it. Simple. I have written an OS GUI like this for the browser, in TypeScript, that scaled easily until all system memory is consumed.