someone who was done with the series will definitely give anyone approval to continue it as he is completely done with it.Lord Kishimoto gave the novel his approval. Therefore making it canon.
Sure it's "canon" but we all know it's fanmade. He just gave it his blessings.
All Kishi's content ended during Sarada's oneshot. Any contributions outside of that is fanmade. Yes that includes those novels.
Basically manga, 2 movies, sarada's oneshot. Those are all canon. Anything outside is just marketing.
So videogames, novels, TV show, that's all fan service.
Hell, that Sarada's ending was also fanservice.
He changed the tone and direction completely when he was implying Karin was the mother and everyone got angry.