How to define index signature for object with string array as key in Typescript

I have a function that returns something like:

function someFunction() {
  return {
    [id]: {
      desc1: desc1,
      desc2: desc2,
    },
  };
}

where I have an interface defined as:

export interface SomeInterface {
  desc1: desc1;
  desc2: desc2;
}

Then I have some code that calls this:

let output: { [key: string[]]: SomeInterface }; // Tried to type it this way but gave an error


output = someFunction() // I have multiple calls to this in the code

However, I get a typescript error on key:

An index signature parameter type must be 'string', 'number', 'symbol', or a template literal type.ts