What is the most efficient way in (functional) React to update a component when a variable changes value?
A piece of code somewhere in the program (over which I have no control) changes a variable e.g. an array in a "Redux" compatible way (i.e. a new reference is returned).
I would like to simulate Redux's useSelector without having to have to use Redux.
Updating the component means you need useState, Not sure what exatcly you are looking for, But if you want to update the component without much Props drilling, then i will suggest you to look into the Context-API on react.
This way you can have control like redux, without redux. https://reactjs.org/docs/context.html