[Solved]-Typescript-React State: Element implicitly has an 'any' type because type 'State' has no index signature-Reactjs

You have to implicitly tell TypeScript that this is the array of the keys of the state.

const SomeFields: Array<keyof State>

This is also improving TS experience as you will get code completion in your editor/IDE when trying to e.g. add an element to SomeFields or use switch etc.