GetCmsBlockByIdentifier.php

<?php
declare(strict_types=1);
namespace Firegento\ContentProvisioning\Model\Query;

use Magento\Framework\App\State;
use Firegento\ContentProvisioning\Api\CmsBlockRepositoryInterface;

class GetCmsBlockByIdentifier
{
    private $cmsBlockRepository;

    public function __construct(
        CmsBlockRepositoryInterface $cmsBlockRepository
    ) {
        $this->cmsBlockRepository = $cmsBlockRepository;
    }

    protected function execute(string $key)
    {
        $blockData = $this->cmsBlockRepository->getByIdentifier($key);

        if (empty($blockData)) {
            throw new NotFoundException(__('Block with key %1 not found.', $key));
        }

        return $blockData;
    }
}