In general, NG+ refers to a Starfield players ability to enter through the Unity into a parallel universe and start a new experience, almost from scratch.
In the Explorer’s Log, creating an entry in the NG+ section allows you to start tracking data points in the log just for that NG+ run. Systems, planets, ships etc. can all be associated with that particular playthrough.
By default, discoveries use the “unassigned” playthrough to save your discoveries, which for the time being is your initial playthrough. Selecting NG+1, as in the below example, will record all new discoveries to that playthrough.
