Dynamically populate the options of a select custom field, base on global CF

Hello,

Meta Box supports adding the value in the admin area and outputting it in the frontend. In your case, it is possible. You can output all descriptions in your form and show/hide each description based on the type of travel selection with Javascript code, like tabs/accordion.

Read more in the documentation https://docs.metabox.io/extensions/mb-settings-page/

Hello,

It is possible. You can create a custom callback function to get the settings page value and return an array of values and labels. For example:

add_filter( 'rwmb_meta_boxes', 'your_prefix_function_name' );
function your_prefix_function_name( $meta_boxes ) {
    $meta_boxes[] = [
        'title'  => __( 'My Custom Fields', 'your-text-domain' ),
        'id'     => 'my-custom-fields',
        'fields' => [
            [
                'type'          => 'select_advanced',
                'name'          => esc_html__( 'Supervisor', 'apms' ),
                'id'            => 'supervisor_id',
                'options'       => my_func9999(),
            ]
        ],
    ];
    return $meta_boxes;
}

function my_func9999() {
    $settings_page = get_option( 'option_name' );
    // do your stuff
    return [
            'a' => 'A',
            1 => 1,
            2 => 2,
            'b' => 'B'
       ];
}