By default, the pinch & zoom functions are disabled on Divi websites. This should be enabled to meet accessibility guide lines.

There are various ways to do this:

1. In the functions.php of a child theme

// Enable Pinch & Zoom
https://help.elegantthemes.com/en/articles/2190905-how-to-enable-pinch-to-zoom-on-mobile
function remove_my_action() {
  remove_action('wp_head', 'et_add_viewport_meta');
}
function dt_et_add_viewport_meta(){
  echo '<meta name="viewport" content="width=device-width, initial-scale=1.0, maximum-scale=5.0, user-scalable=1, viewport-fit=cover" />';
}
add_action( 'init', 'remove_my_action');
add_action( 'wp_head', 'dt_et_add_viewport_meta' );
Code language: PHP (php)

2. Divi theme options » integrations

Add the following to the head section in Divi » Theme options » integrations.

<meta name="viewport" content="width=device-width,
initial-scale=1.0, maximum-scale=5.0, user-scalable=1" />
Code language: HTML, XML (xml)

Source: https://intercom.help/elegantthemes/en/articles/2190905-how-to-enable-pinch-to-zoom-on-mobile