TYPO3 Core

Seems to have another reason: #96371

This is also a serious problem when using an early frontend middleware which uses extbase repositories (injected through DI).
If the middleware is executed before typo3/cms-frontend/prepare-tsfe-rendering then the global Request Object $GLOBALS['TYPO3_REQUEST'] is not set and therefore the Backend Configuration Manager is used.

This should be fixed, especially if the middleware is created explicitely as frontend middleware, the configuration manager should then resolve to the frontend configuration manager.

The main problem is that the $GLOBALS['TYPO3_REQUEST'] object is set too late (in PrepareTypoScriptFrontendRendering middleware). Currently, I overcome this problem with a 'helper' middleware registered early in the frontend, which sets the request object:

   public function process(ServerRequestInterface $request, RequestHandlerInterface $handler): ResponseInterface
    {
        $GLOBALS['TYPO3_REQUEST'] = $request;

        return $handler->handle($request);
    }

@Christin Gmeiner I can confirm that this fix works, I just implemented it myself and now the FE plugin (from EXT:solr) is working as expected.