I think every new user account should be automatically subscribed the the
Announcements ->Stable Updates forum.
This is a crucial part of following Manjaro updates as often people will miss important information if they do not read these threads. Like recently the Nvidia incompatibility with Kernel 5.9 but also when there is manual intervention required to not break the login system or things like that.
There might be other important defaults to modify but I think this is one of the most important. User can always opt-out if he wants but he can not then say he didn’t know, it would be on him.