The current extension has been updated for Flarum 2.x, but will be under Minimal Maintenance as the main feature is merged into 2.x core extension, and I dont really see a proper use case for following all discussion being read.
Also if you are wondering how to set default value for FollowAfterCreate, a PR had been created in fof/default-user-preferences FriendsOfFlarum/default-user-preferences25 for managing the default value of FollowAfterCreate in 2.x but havent been merged yet