Yup, form tags aren’t among WordPress’s global accepted HTML tags. Sliders aren’t designed for you to put all of this into their descriptions. If you’d like to add form tags in, this would be a customization you’d need to make.
You can filter them through the theme like this:
Alternatively, you could also just remove all sanitization for those textareas if you wanted.
remove_all_filters( 'of_sanitize_textarea' );
Currently you aren’t using a Child theme, but in order to do any of these things you’d need to install a Child theme and then these various option would happen from your Child theme’s functions.php.