this will add the approval event to gravityforms notifications and then send that approval notification upon approval via GravityView.

GravityViewEmailOnApproval.php

add_filter( 'gform_notification_events', 'gw_add_manual_notification_event' );
function gw_add_manual_notification_event( $events ) {
    $events['su_approval'] = __( 'Send Approval' );
    return $events;
}

add_action('gravityview/approve_entries/approved','su_send_approval');
function su_send_approval($entry_id){
    
    $entry = RGFormsModel::get_lead($entry_id);
    $event = 'su_approval';
    $form_id = $entry['form_id'];
    $form = GFAPI::get_form( $form_id );
    $notification = GFCommon::get_notifications_to_send( $event, $form, $entry );

    $notifications_to_send[] = $notification[0]['id'];

    GFCommon::send_notifications( $notifications_to_send, $form, $entry, true, $event );
}