custom field readonly not working with taxonomy

Hello,

I created a custom field taxonomy but even though I made it readonly this value is not honored. This happens whether or not I make the field select2. All agents can edit the field.

wpas_add_custom_field( 'cars',
    array(
    'title' => 'Car',
    'field_type' => 'taxonomy',
    'taxo_std' => false,
    'label' => 'Car',
    'label_plural' => 'Cars',
    'order' => 3,
    'required' => true,
    'select2' => true,
    'readonly' => true,
    'show_column' => false,
    'sortable_column' => false,
    'filterable' => false,
    'taxo_hierarchical'     => false,
    'column_callback'       => 'wpas_show_taxonomy_column',
    'update_count_callback' => 'wpas_update_ticket_tag_terms_count',
  )
);

I have two additional questions:

is there any difference between using wpas_add_custom_field or wpas_add_custom_taxonomy when the field_type is ‘taxonomy’?

can custom fields (even if added with the plugin) be managed by other plugins such as the power pack security profiles?

Thanks