Kirby 3.6.1 with Algolia indexing kirby collection possible?

I am using the Algolia plugin / way of indexing from the kirby Github repo at GitHub - getkirby/ Source code and content for the Kirby website

Until now I had only used $page in the config.php like here:

return [
    'algolia' => [
        'app'   => 'XXXXXXXX',
        'key'   => $key,
        'index' => 'kirby',
        'fields' => [
            "url" => function($page) {
                return $page->url();

My issue now is, I need to include the urls and contents of files in the index.
The files should appear in the search as their own items.

To get everything in one place I have a kirby collection with all pages and files in one array.
But I am a bit unsure as to how to include it in the config for it to be indexed into Algolia.
If I add the necessary keys to my kirby collection, can I simply pass that to the ‘fields’ here instead of using function($page) for every key?

Without being very familiar with the plugin, from a brief look I can see that it only indexes pages ($site->index()), so I don’t think this will work without modifying the plugin.