Cloud Firestore: Update fields in nested objects with dynamic key

I found the solution inspired by a firebase solution (replacing "/" by ".").

var usersUpdate = {};
usersUpdate[`favorites.${key}.color`] = true;

db.collection("users").doc("frank").update(usersUpdate);

This solution worked for me:

db.collection('users').doc('frank').update({
  [`favorites.${key}.color`]: true
});