Which is strange, because they are found during the build step, and the project builds without issue. It works locally when running next dev and the open graph tab in vercel shows no issues.

⨯ Error: ENOENT: no such file or directory, open '/var/task/apps/app/assets/Montserrat-Regular.ttf'
    at async f (.next/server/app/opengraph-image/route.js:1:1750) {
  errno: -2,
  code: 'ENOENT',
  syscall: 'open',
  path: '/var/task/apps/app/assets/Montserrat-Regular.ttf'
}

The file apps/app/assets/Montserrat-Regular.ttf certainly exists at build time. But in prod at runtime, it error500's with the above issue.

export default async function Image({
  params: { league_id },
}: {
  params: { league_id: string };
}) {
  // Font loading, process.cwd() is Next.js project directory
  console.log(process.cwd());
  const MontserratRegular = await readFile(
    join(process.cwd(), "assets/Montserrat-Regular.ttf"),
  );