Topic on User talk:Nummer378
Yeah through some googling I saw that this is one of a few common EOS/EGS flags. I did walk through the most recent version downloaded from EGS and this flag isn't read anywhere.
I did perform tests in a VM where EGS wasn't even installed, so there was nothing in the background.
You can actually find documentation on these flags in Epic's developer resources: https://dev.epicgames.com/docs/epic-account-services/auth/auth-interface
The code that launches the EGL when -EpicPortal is missing is most likely this function: https://dev.epicgames.com/docs/game-services/eos-platform-interface#restarting-the-app-with-the-launcher - Frostpunk never calls this function. In fact, I was unable to trigger a launch of the EGL with Frostpunk at all. If authentication is not overriden, it does fail Epic auth and then terminates, but it never launches the launcher.
This might have been different for older versions from the game, but since the entire EOS integration in Frostpunk appears custom, I suspect it has always been this way.