Check the action
of the current screen object for add
:
function wpd_add_meta_box() {
$screen = get_current_screen();
if( 'add' != $screen->action ){
add_meta_box(
'myplugin_sectionid',
'My meta box',
'myplugin_meta_box_callback',
'leads'
);
}
}
add_action( 'add_meta_boxes', 'wpd_add_meta_box' );