Actually, it’s not ACF, it’s your browser. I just created a form outside of WP and tested an email field and my browser would not let me submit it. I searched the ACF code and could not find anything in ACF doing validation of email fields. I suspect that ACF is tying into the browser’s built in validation of these fields.
I could be wrong and you might want to contact the developer. https://www.advancedcustomfields.com/contact/
I’d probably use a text field and do my own validation it this was required
