I have a getURL() function that always used to work in prod and locally, that I would pass to robots.ts, sitemap.ts and things like better-auth and Polar.sh but since upgrading to Next.js 16 few hours ago I noticed that both on Vercel and self hosted apps the resolved URL is always http://localhost:3000 and the env variables get skipped on all of those mentioned prod environments:

export const getURL = () => {
  let url =
    process?.env?.NEXT_PUBLIC_VERCEL_PROJECT_PRODUCTION_URL ?? // Automatically set by Vercel.
    process?.env?.NEXT_PUBLIC_VERCEL_BRANCH_URL ?? // Automatically set by Vercel.
    process?.env?.NEXT_PUBLIC_VERCEL_URL ?? // Automatically set by Vercel.
    'http://localhost:3000';
  // Make sure to include `https://` when not localhost.
  url = url.includes('http') ? url : `https://${url}`;
  // Make sure to exclude trailing `/`.
  url = url.charAt(url.length - 1) === '/' ? url.slice(0, -1) : url;
  return url;
};

I went over the changelogs and can't figure out what changed that would cause this to stop working in all of the places in the codebase.