TYPO3 Core

StandaloneView uses ContentObjectRender ("cObj") e.g. to have stdWrap functionality in place.
In case you're not using page-related or TypoScript-related functionality, switching to TemplateView seems to be the better alternative.

TemplateView is more or less workable. The problem is that as soon as I use f:translate in my template the view can't be rendered. I have tried with key="LLL:EXT:myext/Resources/Private/Language/locallang.xlf:key1" but it does not help.

I managed to get TemplateView working by calling it this way:
$this->objectManager=GeneralUtility::makeInstance(ObjectManager::class);
$context = $this->objectManager->get(RenderingContext::class, $this);
$request = $this->objectManager->get(WebRequest::class);
$request->setRequestUri(GeneralUtility::getIndpEnv('TYPO3_REQUEST_URL'));
$request->setBaseUri(GeneralUtility::getIndpEnv('TYPO3_SITE_URL'));
$request->setControllerExtensionName('extensionname');
$controllerContext = $this->objectManager->get(ControllerContext::class);
$controllerContext->setRequest($request);
$uriBuilder = $this->objectManager->get(UriBuilder::class);
$uriBuilder->setRequest($request);
$controllerContext->setUriBuilder($uriBuilder);
$context->setControllerContext($controllerContext);

$this->view=GeneralUtility::makeInstance(TemplateView::class);
    $this->view->setRenderingContext($context);

In fact I copied most of the code of the __construct of StandaloneView. So I made more or less the 9.5 version of StandaloneView. I don't know it this is the intention of the developers of the StandaloneView.

Bug exists also, if you want to send an email from an eID Middleware with FluidEmail.
The view property of FluidEmail is a StandaloneView as well.