How to get user regional settings in a browser? Not user language

My Windows11 language is english but my regional settings is set to danish.

When I run the below code ‘en-GB’ is returned. I expected ‘da-DK’ to be returned.

    function getUserLocale() {
        const intl = window.Intl;
        if (intl !== undefined) {
            return intl.NumberFormat().resolvedOptions().locale;
        }

        // Old standard.
        return navigator.language ?? "en-US";
    }