Found a typo in stripe_webform_payment/src/StripteWebformPaymentWebform.php.
The href property in the opening <a> html tag is not closed properly, and this turns the whole YAML textarea into a link so when you try to click into it in the UI, the link opens instead. (And it's a broken link because of the > appended.)
$form['stripe']['appearance_container']['stripe_appearance'] = [
...
'#description' => $this->t("You can customize your Stripe Payment elements appearance. Please refer to <a href='https://stripe.com/docs/elements/appearance-api>'Stripe appearance API</a> for more details."),
...
];Patch coming right up.
Fixed
1.0
Code