A common writing tool is to use a story grid. You have chapters/similar along the Y axis and title, characters, plot elements, etc. along the X axis. That way you can keep track of what information you are revealing at each story beat/chapter, make sure that plot twists work (e.g. when outlining something like The Sixth Sense).

Depending on how big the story is and how many characters/plot threads there are, I can see the Excel files getting large.

There are already tons of specialist non-AI tools for writers to be able to keep track of story elements, research, etc.

Writers (older genre writers particularly) tend to be a bit behind the technological curve, and they stick with whatever works. If you want to see a treasure trove of "old web" sites, look up the site of any sci-fi or fantasy author. Chances are its design and layout still look like something from the late 90s.

The vast majority of AI apps don't actually solve any novel problems (pun intended come at me,) they're just new versions of existing solutions "but with AI."