Apologies if I’m misunderstanding anything since I haven’t personally done the Weird Route in Deltarune, but based on what I've seen so far, Chapters 2, 4, and 5 appear to be the ones connected to the weird route. However, the weird route only seems to extend up to Chapter 5. However, I don’t think this means the Weird Route ends in Chapter 5 like some theory's I've seen online. Instead, I think Chapter 5 is simply the final opportunity to abandon it.

In Chapters 2 and 4, you can prevent the Weird Route from progressing, either by not making Noelle strong enough in Chapter 2, or by stopping yourself before putting the Thorn Ring on her in Chapter 4 making her think it was just a prank. Because of that pattern, I believe Chapter 5 will be the last point where the player can choose to step off the Weird Route. If you don’t, then you’re locked into it for the rest of the game. It would mirror how Undertale’s Genocide Route works: you can abandon it at any time however once you killed the final monster, your committed to it.

Because of this, I think Chapter 5 is essentially the final monster. Your decision to kill it or not, determines whether you’re permanently locked into the Weird Route or able to return to the normal route.

Do you think the photo means that after Chapter 5 you can no longer abandon the weird route?