Use User Profile Data as Default Data for Other MB Custom Fields

Hi,

If you have the field number for the user and it has the ID fav_number, then you can use this code to get the user meta and set it as the default value when registering the field number for the post.

add_filter( 'rwmb_meta_boxes', 'your_prefix_function_name' );
function your_prefix_function_name( $meta_boxes ) {
    $current_user_id = get_current_user_id();
    $default_number = get_user_meta( $current_user_id, 'fav_number', true );

    $meta_boxes[] = [
        'title'  => __( 'Post Meta', 'your-text-domain' ),
        'id'     => 'post-meta',
        'fields' => [
            [
                'name'       => __( 'Number', 'your-text-domain' ),
                'id'         => 'number',
                'type'       => 'number',
                'std'        => $default_number
            ],
        ],
    ];
    return $meta_boxes;
}

Refer to the documentation
https://developer.wordpress.org/reference/functions/get_user_meta/
https://docs.metabox.io/field-settings/#default-value