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

Question

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.

Answer 1

Because of the terrible after effects. Against Kaguya, they had better alternatives. And Naruto had many other cards up his sleeve too.

Answer 2

In the series, because they didnt want to just sacrifice. Thought it´s "suspicious" Kurama didn´t even mention the ability those years back, considering how powerful was Kaguya.

In a meta sense, thats just because it is a invented power-up, which was just recently retconned into existing. So Naruto didnt used it and Kurama didnt mention it against Kaguya, because Kishimoto hadnt even thought about it yet. Also, stop for a moment and think: how someone like Kurama even knows what nuclear fusion is? We know Naurto is an idiot and doesnt know, but he is also the hokage, so how a chakra beast knows the term while he doesnt? It´s kurama reading science books in his free time or what...?