Sage, Gutenberg and ACF Blocks

1.)
Any ideas how I can solve this error?

Fatal error: Uncaught Error: Class 'Itineris\AcfGutenblocks\Plugin' not found in /app/public/wp-content/plugins/acf-gutenblocks/acf-gutenblocks.php:32
Stack trace:
#0 /app/public/wp-includes/class-wp-hook.php(286): Itineris\AcfGutenblocks\{closure}('')
#1 /app/public/wp-includes/class-wp-hook.php(310): WP_Hook->apply_filters('', Array)
#2 /app/public/wp-includes/plugin.php(465): WP_Hook->do_action(Array)
#3 /app/public/wp-content/plugins/advanced-custom-fields-pro/acf.php(334): do_action('acf/init')
#4 /app/public/wp-includes/class-wp-hook.php(286): ACF->init('')
#5 /app/public/wp-includes/class-wp-hook.php(310): WP_Hook->apply_filters(NULL, Array)
#6 /app/public/wp-includes/plugin.php(465): WP_Hook->do_action(Array)
#7 /app/public/wp-settings.php(525): do_action('init')
#8 /app/public/wp-config.php(76): require_once('/app/public/wp-...')
#9 /app/public/wp-load.php(37): require_once('/app/public/wp-...')
#10 /app/public/wp-blog-header.php(13): require_once('/app/public/wp-...')
#11 /app/public/index.php(17): require('/app in /app/public/wp-content/plugins/acf-gutenblocks/acf-gutenblocks.php on line 32

I put the following code into my setup.php:

add_filter('acf_gutenblocks/blocks', function (array $blocks): array {
    $new_blocks = [
        Testimonial::class,
    ];
    return array_merge($blocks, $new_blocks);
});

If I remove the code above, my application works correctly.

2.)
Also, do I define ACF fields inside of the controller for the block? So, for example, add to app/blocks/testimonial/testimonial.php the protected function registerFields(): array {} code?