For initial authentication, where should an app try reading PlayerPrefs data? in Start()? or another clause?
Does this vary depending on platform? Would it be a different location in mobile vs desktop?
authentication? I’m not sure what you mean but you can read PlayerPref(erence)s anytime you like.
The useage of PlayerPref should be equal on all platforms.
I suggest to actually read what is written on this page. PlayerPrefs is a method to transparently store preferences, it actually shouldn’t matter where it’s stored.