Not a mod, but typically how it works it you do the run and submit it, and the category will be made as a result.

There's been a NG+ run already but I'm not sure if it was submitted.

First and foremost. Just because there isn't a category on the leaderboards doesn't stop you from running whatever you want in the end. At the same time, just because someone does a run of "something" doesn't automatically mean it will get added to the leaderboards just because it exists. There's been a lot of discussion about it in the past regarding Persona 5 already. Refer to Liv's post in this thread: https://www.speedrun.com/persona_5_royal/thread/90ide/1#rsy6f - It sums up some of the points regarding categories, even outside of NG+.