can u provide a codesandbox?

Sure thing: https://codesandbox.io/s/javascript-forked-h5d7yz?file=/src/index.js

It seems like the issue comes from this particular call:

import { shouldPolyfill } from "@formatjs/intl-displaynames/should-polyfill";

const foo = shouldPolyfill("fr");

With 6.6.1 I am getting foo = "fr" which is expected.
With 6.6.2 I am getting foo = "br" which is the short code for a regional French language (breton). This is not correct.

Because of this bug my app is not loading @formatjs/intl-displaynames/locale-data/fr.

Long story short, I had to replace:

const foo = shouldPolyfill("fr");
await import(`@formatjs/intl-displaynames/locale-data/${foo}`);

by:

const foo = shouldPolyfill("fr");
await import(`@formatjs/intl-displaynames/locale-data/fr`);

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

As far as I know this issue is not resolved, and should not be closed.

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

kk this issue is due to the list of supportedLocales is assumed to be ordered which for polyfills they aren't. Will fix soon.

For posterity, the problem is the list of supported locales have both br & fr but was sorted alphabetically. fr - br has a match score of 250 but because fr's index was more than 250 below br, the penalty kicks in and knock it down to 259.