All Fortnite sessions require members to connect their Epic account to GeForce NOW. Account linking has a number of benefits including automatic Fortnite sign in, synchronized game progress, and faster launch times.
To manage connected accounts, launch the GeForce NOW app and go to Settings > Connections > Epic Games:
Members that complete Epic Account Linking get a feature called pre-loading, which starts loading parts of Fortnite before you start your game stream, so that your game launch times will be faster by up to a minute from clicking play in GeForce NOW, to when you see the Fortnite in-game lobby.
Free members are not guaranteed Fortnite pre-loading and may see slightly longer startup times than Ultimate, Priority and Founders members.