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.