It will be a good practice to use modern
<button type="submit"></button> html semantics instead of
<input type="submit"/> in all frontend forms.
The main reason that WP themes will have more control to customize
<button> elements via CSS. It’s possible add inner HTML content (
<strong> or even
<img>), and make use of
:before pseudo-elements to achieve complex rendering while
<input> only accepts a text value attribute.
At the moment Gravity buttons are presented by
<input type="submit">, this is really outdated in 2020.
Just check how it was in WooCommerce plugin https://github.com/woocommerce/woocommerce/issues/17254