I have been wanting to start running levels, but upon inspection, I am confused at why there is no 100% for each level. Could this happen?

I guess that is because you have to enter every level twice to 100% complete them, once before finishing the game and once post-game. Also Hint arts suck.

its partly because whilst the route you're learning from is porbably Timpani's, there are a variety of different aum routes, which mean people get different moons at different times - meaning even if there were IL's for things like cap 1 and then cap 2, they could have objectively different routes.

However, if you want to run IL's, there is nothing to stop you doing it

Do you mean all moons and all purple coins or just moons. There are also some kingdoms where it is the as any% if it would be 100% npg. And hint arts/ painting moons suck. But it could be fun, mayby on the extensions board?

Cap is an exception together with Cloud, Ruined assuming Ruined 1 only fought the boss, Moon assuming Moon 1 didn't collect any moons and purples, Mushroom if you exclude Toadette and revisits, Dark Side, and Darker Side, but for the other kingdoms there's pretty much no good way to define a "kingdom clear" category. Two AUM runners might do completely different combinations of e.g. Wooded 1 and Wooded 2

In contrast, categories that could work would be All Moons No Revisits (excluding Toadette in Mushroom) or All Purple Coins NG+