I would be interested to hear from anyone who set it and can still access Plex over their LAN in a network outage. I have set this multiple times according to docs, and it worked only once ever, thereafter apparently resetting to online login. Of course, they do not make this an easy setting to change!

You need plex pass to do this now. They changed it recently you didnt used to need it.

I have had lifetime pass about ten years.

The mobile apps require signing in through the Plex website before you can do anything?