This worked for me too. However, I ran into issues with the gallery field. After the first submission, if you get back to the same form, it won’t set the selected media. So, I am use the following code.
add_filter( 'ajax_query_attachments_args', 'wpb_show_current_user_attachments' );
function wpb_show_current_user_attachments( $query ) {
$user_id = get_current_user_id();
if ( $user_id && !current_user_can('activate_plugins') && !current_user_can('edit_others_posts
') ) {
$query['author'] = $user_id;
}
return $query;
}