So if i use (is it correct?) it should work?
function 123_update_user( $post_id )
{
if (strpos($post_id, 'user_') !== 0)
return;
$user_id = intval(substr($post_id, 5));
update_user_meta( $user_id, 'network_public', false);
}
add_action( 'acf/save_post', '123_update_user', 5 );