Reply To: action rwmb_after_{$meta_box_id} or action for settings page

Yes, you can do that with the hook mb_settings_page_load. It's the internal hook used to save the fields' values after the settings page is loaded. The process uses priority 10, so if you want to do something after that, you should use a higher priority, such as 20.

Here is an example:

add_action( 'mb_settings_page_load', function ( $args ) {
    if ( $args['id'] === 'YOUR SETTINGS PAGE ID' ) {
        // Do something
    }
}, 20 );