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