Why didn't Naruto uses his full power that he demonstrated in `Boruto chapter 52` against Sasuke or `Kaguya Ōtsutsuki`


In Boruto _chapter 52_ Naruto demonstrated unsual high power which made him so
much powerful that he almost solely defeated Isshiki Ōtsutsuki.

So if Kurama had this power than why didn't he give that power to Naruto in
his fight against Kaguya.

Naruto power is described as

> Sasuke : Such tremendous chakra. He never told me he had move like this.
> What is it.
>
> Kurama : Think of it like nuclear fusion. It's similar principle to how the
> sun produces energy.
>
> Naruto : Nuclear fusion? What's that?
>
> Kurama : never mind. the theory doesn't matter. My chakra and your chakra
> are serving as the kernels to produce a whole other new type of energy.
> That's all.




In the series, because they didn't want to just sacrifice. Though it´s
"suspicious" Kurama didn´t even mention the ability those years back,
considering how powerful was Kaguya.

In a meta sense, that's just because it is an invented power-up, which was
just recently retconned into existing. So Naruto didn't use it and Kurama
didn't mention it against Kaguya, because Kishimoto hadn't even thought about
it yet. Also, stop for a moment and think: how someone like Kurama even knows
what nuclear fusion is? We know Naruto is an idiot and doesn't know, but he is
also the hokage, so how a chakra beast knows the term while he doesn't? It´s
kurama reading science books in his free time or what...?

