add_filter( 'mastodon_api_public_timeline', function( $statuses, $request ) {
    $args = array( 'post_status' => 'publish' );
    $posts = get_posts( $args );
    $statuses = array();
    foreach ( $posts as $post ) {
        $statuses[] = apply_filters( 'mastodon_api_status', null, $post->ID, array() );
    }
    return new WP_REST_Response( array_filter( $statuses ) );
}, 10, 2 );

\apply_filters( 'mastodon_api_public_timeline', null, $request )