If you’re not married to functional code, for searching a keyed object by property for the key, you can always write:

for (const key in data) {
  if (data[key].firstName === 'Frederic') {
    console.log(key);
  }
}

No need to transform the whole object with Object.entries, and you could turn that into a function reasonably easy, something like findKey(object, property, value) or some such.