"Nur arc" probably just means act 2. It's set in the Nur Empire. It's not being adapted for multiple reasons, but the given reason was that Inori-sensei is afraid of a cancellation happening halfway through... Don't forget, act 1 has taken 5-and-a-half years to adapt, it started in late 2020...
It's a massive shame, because while yeah act 2 has problems, I think an adaptation would be the perfect chance to clean them up.
Also, act 2 is definitely still canon to the manga, at least! There's been a handful of cameos of act 2 characters. Dorothea at the end of chapter 18, DQ in the middle of chapter 55... Rae is seen from behind, but look just a page earlier- her hair is never that long. Kinda a fringe theory but over in the watacord we like to think it's DQ.