You can use the gform_user_registered filter to ADD an additional role to the role you have configured in the User Registration feed.
The code would look like this to add an additional role:
add_action( 'gform_user_registered', 'add_another_role', 10, 3 );
function add_another_role( $user_id, $feed, $entry ) {
// edited code example July 19, 2021 to add the next line
$user = new WP_User( $user_id );
// add another role to the registered user
$user->add_role( 'super-dude' );
}
That code can go into your theme functions.php file or a functionality plugin.