date-fns actually barely uses Intl. Rather, it has custom locale files that must be imported to use: https://date-fns.org/v2.22.1/docs/I18n. There is a single intlFormat function: https://date-fns.org/v2.22.1/docs/intlFormat

Once I realized this I switched to Luxon, which is entirely Intl based: https://moment.github.io/luxon/docs/manual/intl.html