In the end of the Kaguya-sama manga, there were some unexpected plot twists that added excitement. The characters' growth and development reached a conclusive and fulfilling stage. It left fans with a sense of closure and happiness.
In some fanfictions, Naruto might gain the power to defeat Kaguya through intense training in a hidden realm. This realm could have special chakra - enhancing properties that allow him to reach new levels of power.
Kaguya-sama's third season ended at a point in the manga that's a bit tricky to define exactly. It roughly corresponds to a particular storyline, but for the exact chapter, you'd have to do some digging on manga-related communities or resources.