vercel: what conditions need to be met for the following serverless functions to be created?

[UltraCakeBakery]

I am trying to debug an issue where my color-chunk-[chunkX]-[chunkY]-[chunkSize]/+server.ts route returns a 404 on vercel. I think it has to do with that there is a custom serverlessfunction being generated for it, and that it somehow isn't mapped correctly? I'm not sure entirely sure, but I hope to get a better understanding of what happens internally so I can properly debug this.

I remember reading somewhere that __data.json routes are no longer a thing / being used in SvelteKit? Is that true?

And why is this ISR route separated into its own function? Can't it be part of the standard singular render function?