add_filter(
   'friends_get_activitypub_metadata',
    function(
        array $array,
        $actor_url
    ) {
        // Your code here.
        return $array;
    },
    10,
    2
);

apply_filters( 'friends_get_activitypub_metadata', array(), $actor_url )

apply_filters( 'friends_get_activitypub_metadata', array(), $feed_details['url'] )