With MobX + React, how can I initialize state without triggering a state update?

Question

I have a settings store

class SettingsStore {
  crosshairPosition
  constructor() {
    makeAutoObservable(this);
  }
}

and an effect which save settings to the cloud when they are updated

useEffect(() => reaction(
  () => settings.crosshairPosition, 
  () => cloud.save(settings.crosshairPosition)
), []);

Unfortunately the reaction triggers when I load the settings from the cloud on app startup, because the MobX store changes at that time. How should I restructure my application to avoid the state update on first load?