What is the documentation issue?

https://nextjs.org/docs/pages/api-reference/next-config-js mentions the next.config.mjs extension as well as using the TypeScript next.config.ts. I know this is likely PEBKAC, but with the Next.js 14 default being next.config.mjs, I assumed that I could be explicit and change this to next.config.mts.

However, running next build actually ignores this file without complaints and assumes the defaults as if this file doesn't exist. For example, setting this in next.config.mts

  distDir: 'standalone-build',
  output: 'standalone',

is ignored and the build is created in the .next directory.

Is there any context that might help us understand?

I'm not sure of the proper solution, but one of

1. Provide a footnote that next.config.mts isn't supported and will be ignored
2. If next.config.mts support is planned for, provide a note in the documentation.
3. If next.config.mts support was expected to work, turn this documentation issue into a bug.
4. Check for next.config.mts and provide a build log if found on how to resolve

Does the docs page already exist? Please link to it.

https://nextjs.org/docs/pages/api-reference/next-config-js