From those same docs, it appears you can build an API with Route Handlers when using Server Components:

https://nextjs.org/docs/app/building-your-application/routin...

Correct. It can also run during the build, so it can be used to dynamically generated .txt, .json, or any other files. Great when deploying a static export of Next.js and dumping on S3 or similar.

https://nextjs.org/docs/app/building-your-application/deploy...

Do you know what an api is?