in every chapter since chapter 1 we've learned something about the dark worlds work or the knight.
Chapter 2: we learn about the roaring
Chapter 3: we meet the knight
Chapter 4: we learn that dark worlds can being monster remains back to life, we see a titan, the knight can ignore game hacks/code editing (whatever Flowery does, i don't remember if his code editing gets a name)
In chapter 5 we learn something bad happened & Asgore thinks it happend because of a dark word, this is about a dark world & not dark worlds as a whole.
We also learna shelter code, & yes that is BIG but it doesn't tell us anything story wise. We knew he was involved because of the scenes we see in the vents at Noelles house. In the story it is a big deal, it is in fact a big reveal, but it doesn't actually tell us anything new like the previous chapters have.
(also also because it doesn't contain 122 we can guess the code is super long & we'll need to combine all of them, or there are multiple shelters! very interesting & i'm looking foward to seeing some theories about this.)
One thing that could be major is if my first thought about the lake scene (sowgrave/weird route) is correct, Noelle says Dess "left" why would she say that if it was well known that Dess got kidnapped, or died, ect. In the normal route Noelle ends up talking about she wishes she could run away, saying she thinks about what would happe "if [she] left"
This makes me think that Dess ran away, or Noelle thinks she ran away. Wich is also interesting because we can assume the reason Asgore is fixated on the dark worlds is because someting really horrible happened, & while Dess running away is concerning it's not the worst thing that could cause her to go missing. (& if you're wondering about her room having all her stuff, it's possible that Dess told Noelle & no one else that she was running away, maybe she didn't take anything with her on purpose to trick everyone.)
[ID: Noelles yellow child sprite in a black void, a text-box says "Since Dess left..." end ID]
[ID: Susie holding Noelle while standing in the lake at sunset, a text-box with Noelle's talking sprite says "I've actually been thinking about..." end ID]
[ID: the same scene, the text-box now says "What would happen... If I left." end ID]