brokenRecord.ts

type Keys = 'a' | 'b';
type Data = Record<Keys, string>;

function getSomeKey(): Keys {
  return 'a';
}

const data: Data = {
  a: 'hello',
  b: 'world',
};

const dataUpdated = {
  ...data,
  [getSomeKey()]: 5,
};

console.log('results', data, dataUpdated);