If you're logged in and change the postal code in the stripe widget, it appears to update in the billing fields section, but does not update in civi.
Semi-related, maybe: #247
I haven't tested yet but I think the problem is here because it sets it to
disabled, and disabled html fields are not included in $_POST: https://lab.civicrm.org/extensions/stripe/-/blob/0e7645da79d14140d23ddd9c3127f966a59c0042/js/civicrm_stripe.js#L618-621
readonly attributes do submit, but I think the styling varies.