TYPO3 Core

Extbase is bound to frontend requests, specifically it needs TypoScript to setup persistence atrributes.

The linked issue is a request to make bootstrapping a custom frontend request easier to set up.

For now you can use something along these lines (from Christoph Erdmann via slack typo3-cms):

private function initCliEnvironment(): void
{
    if (PHP_SAPI === 'cli') {
        $this->classesConfigurationFactory->createClassesConfiguration();

        Bootstrap::initializeBackendAuthentication();

        /** @var SiteFinder $siteFinder */
        $siteFinder = GeneralUtility::makeInstance(SiteFinder::class);
        $site = $siteFinder->getSiteByIdentifier('your-site');
        $language = $site->getLanguageById(0);
        $GLOBALS['BE_USER']->user['lang'] = $language->getLocale()->getLanguageCode();

        $serverRequest = new ServerRequest();
        $serverRequest = $serverRequest->withAttribute('extbase', []);
        $serverRequest = $serverRequest->withAttribute('applicationType', SystemEnvironmentBuilder::REQUESTTYPE_BE);
        $serverRequest = $serverRequest->withAttribute('language', $language);
        $this->configurationManager->setRequest($serverRequest);
    }
}

Or the code of the linked issue as an example.

Another possibility is to maybe utilize the QueryBuilder to access data you need
In CLI context (for reading) or DataHandler (for writing)

Hope that helps, I'm closing this in favor of the other open issue.