Undici v7(+?) Request cannot parse FormData from Undici v5 #4285

Bug Description

I'm trying to construct a Request with a FormData body, using the global Request in Node.js v24 (which seems to be Undici 7.10.0), but a FormData imported from Undici 5.28.5.

Reproducible By

import { FormData } from 'undici';

const r = new Request('https://example.com', {
  body: new FormData(),
  method: 'POST',
});

console.log(r.headers.get('content-type'));

This outputs multipart/form-data in Node.js 20 & 22, but text/plain in Node.js 24

Additional context

This may well be expected behaviour! However, if it is I would've expected to see some documention mentioning that Undici 5 isn't supported in Node.js 24+.