For a Fairphone or Shiftphone sold as Murena in the store, is e/OS pre-installed directly from the factory without going through ShiftOS or Fairphone OS, or did it come with Android and then go through an unlocking/flashing/relocking process?
And consequently, which OS will restore it to when using a factory reset?
The operating system will not revert to another operating system when doing a factory reset. All personal data and personally added apps will be deleted, but the operating system will stay the same as the most recent version that it was on before the factory reset.
As to when /e/OS is installed on a new phone, I only know for certain that Fairphones come from the final assembly in Shenzhen, China with Android OS (Fairphone’s google-certified Android) installed. The Fairphone 6 with /e/OS pre-installed sold in the Fairphone shop is flashed with /e/OS after arrival in Europe. For the Murena shop, I do not know for sure, but in the past they were also flashed in Europe, so not in the final assembly in the Shenzhen factory.