If you want to enable pinch to zoom on mobile, you need to place this code in a child theme's functions.php file:
function remove_my_action() {
remove_action('wp_head', 'et_add_viewport_meta');
}
function custom_et_add_viewport_meta(){
echo '<meta name="viewport" content="width=device-width, initial-scale=1.0, maximum-scale=2.0, user-scalable=1" />';
}
add_action( 'init', 'remove_my_action');
add_action( 'wp_head', 'custom_et_add_viewport_meta' );
The depth of the zoom can be controlled from this part:
maximum-scale=2.0
For a deeper zoom, change the value to 2.5, 3.0, etc.