❗️Что будет на выходе:

const user = {
  profile: {
    name: "Alice",
    settings: null
  },
  getPreferences() {
    return this.profile.settings?.theme || "default";
  }
};

const admin = {
  profile: {
    name: "Admin"
  },
  getPreferences() {
    return this.profile.settings?.theme || "default";
  }
};

console.log(user.getPreferences());
console.log(admin.getPreferences());
console.log(user.profile.extra?.id?.toString());

Ответ:
default default undefined

JavaScript test | #JavaScript