The sort order can be determined by passing a SortProvider in options.ts.

export type Options = {
  // other options
  sortProvider?: SortProvider<Awaited<ReturnType<typeof bundleMDX>>>;
};

export type SortProvider<
  T extends { frontmatter: UnknownFrontMatter } = {
    frontmatter: UnknownFrontMatter;
  },
> = (pages: T[]) => T[];