ご指摘の通り
/var/www/html/ec-cube/app/Plugin/の配下にProductReview4がなかったため以下コマンドにてインストールを行いました。

bin/console eccube:composer:require ec-cube/<PluginCode>

その後プラグインを有効化したところ、
画面が「システムエラーが発生しました。」
というエラーが出力され、真っ白になりました。

発生当時のエラー内容(admin-2022-08-07.log)を添付します。
もし以下内容より、問題点が分かればご教示いただけると嬉しいです。

[2022-08-07 11:07:33] admin.ERROR [N/A] [6ac3840] [N/A] [Eccube\Log\Logger:log:64] - システムエラーが発生しました。 ["The file \"../../../../PluginData/SiteKit/routes.yaml\" does not exist (in: \"/var/www/html/ec-cube/app/Plugin/SiteKit/Resource/config\", \"/var/www/html/ec-cube/src/Eccube\", \"/var/www/html/ec-cube/src/Eccube/Resources\") in ../../../../PluginData/SiteKit/routes.yaml (which is being imported from \"/var/www/html/ec-cube/app/Plugin/SiteKit/Resource/config/routes.yaml\").","/var/www/html/ec-cube/vendor/symfony/config/Loader/FileLoader.php",168,"#0 /var/www/html/ec-cube/vendor/symfony/config/Loader/FileLoader.php(90): Symfony\\Component\\Config\\Loader\\FileLoader->doImport()\n#1 /var/www/html/ec-cube/vendor/symfony/routing/Loader/YamlFileLoader.php(161): Symfony\\Component\\Config\\Loader\\FileLoader->import()\n#2 /var/www/html/ec-cube/vendor/symfony/routing/Loader/YamlFileLoader.php(91): Symfony\\Component\\Routing\\Loader\\YamlFileLoader->parseImport()\n#3 /var/www/html/ec-cube/vendor/symfony/config/Loader/FileLoader.php(153): Symfony\\Component\\Routing\\Loader\\YamlFileLoader->load()\n#4 /var/www/html/ec-cube/vendor/symfony/config/Loader/FileLoader.php(90): Symfony\\Component\\Config\\Loader\\FileLoader->doImport()\n#5 /var/www/html/ec-cube/vendor/symfony/routing/Loader/GlobFileLoader.php(32): Symfony\\Component\\Config\\Loader\\FileLoader->import()\n#6 /var/www/html/ec-cube/vendor/symfony/routing/RouteCollectionBuilder.php(373): Symfony\\Component\\Routing\\Loader\\GlobFileLoader->load()\n#7 /var/www/html/ec-cube/vendor/symfony/routing/RouteCollectionBuilder.php(62): Symfony\\Component\\Routing\\RouteCollectionBuilder->load()\n#8 /var/www/html/ec-cube/src/Eccube/Kernel.php(194): Symfony\\Component\\Routing\\RouteCollectionBuilder->import()\n#9 /var/www/html/ec-cube/vendor/symfony/framework-bundle/Kernel/MicroKernelTrait.php(87): Eccube\\Kernel->configureRoutes()\n#10 /var/www/html/ec-cube/vendor/symfony/routing/Loader/ObjectRouteLoader.php(65): Eccube\\Kernel->loadRoutes()\n#11 /var/www/html/ec-cube/vendor/symfony/config/Loader/DelegatingLoader.php(40): Symfony\\Component\\Routing\\Loader\\ObjectRouteLoader->load()\n#12 /var/www/html/ec-cube/vendor/symfony/framework-bundle/Routing/DelegatingLoader.php(70): Symfony\\Component\\Config\\Loader\\DelegatingLoader->load()\n#13 /var/www/html/ec-cube/vendor/symfony/framework-bundle/Routing/Router.php(56): Symfony\\Bundle\\FrameworkBundle\\Routing\\DelegatingLoader->load()\n#14 /var/www/html/ec-cube/vendor/symfony/routing/Router.php(371): Symfony\\Bundle\\FrameworkBundle\\Routing\\Router->getRouteCollection()\n#15 /var/www/html/ec-cube/vendor/symfony/routing/Router.php(289): Symfony\\Component\\Routing\\Router->getMatcherDumperInstance()\n#16 /var/www/html/ec-cube/vendor/symfony/config/ResourceCheckerConfigCacheFactory.php(43): Symfony\\Component\\Routing\\Router->Symfony\\Component\\Routing\\{closure}()\n#17 /var/www/html/ec-cube/vendor/symfony/routing/Router.php(302): Symfony\\Component\\Config\\ResourceCheckerConfigCacheFactory->cache()\n#18 /var/www/html/ec-cube/vendor/symfony/routing/Router.php(256): Symfony\\Component\\Routing\\Router->getMatcher()\n#19 /var/www/html/ec-cube/vendor/symfony/http-kernel/EventListener/RouterListener.php(113): Symfony\\Component\\Routing\\Router->matchRequest()\n#20 /var/www/html/ec-cube/vendor/symfony/event-dispatcher/EventDispatcher.php(214): Symfony\\Component\\HttpKernel\\EventListener\\RouterListener->onKernelRequest()\n#21 /var/www/html/ec-cube/vendor/symfony/event-dispatcher/EventDispatcher.php(44): Symfony\\Component\\EventDispatcher\\EventDispatcher->doDispatch()\n#22 /var/www/html/ec-cube/vendor/symfony/http-kernel/HttpKernel.php(127): Symfony\\Component\\EventDispatcher\\EventDispatcher->dispatch()\n#23 /var/www/html/ec-cube/vendor/symfony/http-kernel/HttpKernel.php(68): Symfony\\Component\\HttpKernel\\HttpKernel->handleRaw()\n#24 /var/www/html/ec-cube/vendor/symfony/http-kernel/Kernel.php(200): Symfony\\Component\\HttpKernel\\HttpKernel->handle()\n#25 /var/www/html/ec-cube/index.php(78): Symfony\\Component\\HttpKernel\\Kernel->handle()\n#26 {main}"] [GET, /*/store/plugin, **.**.**.**, https://**/store/plugin, Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/104.0.0.0 Safari/537.36]
[2022-08-07 11:07:33] admin.INFO [N/A] [6ac3840] [N/A] [Eccube\Log\Logger:log:64] - LOGIC END [null] [GET, /*/store/plugin, **.**.**.**, https://****//store/plugin, Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/104.0.0.0 Safari/537.36]
[2022-08-07 11:07:33] admin.INFO [N/A] [6ac3840] [N/A] [Eccube\Log\Logger:log:64] - YamatoSubscription event onKernelResponse start [] [GET, /*/store/plugin, **.**.**.**, https://****/store/plugin, Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/104.0.0.0 Safari/537.36]
[2022-08-07 11:07:33] admin.INFO [N/A] [6ac3840] [N/A] [Eccube\Log\Logger:log:64] - YamatoSubscription event onKernelResponse end [] [GET, /*/store/plugin, **.**.**.**, https:///****/store/plugin, Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/104.0.0.0 Safari/537.36]
[2022-08-07 11:07:33] app.INFO [N/A] [6ac3840] [N/A] [Eccube\Log\Logger:log:68] - PROCESS END [null] [GET, /*/store/plugin, **.**.**.**, https://****/store/plugin, Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/104.0.0.0 Safari/537.36]
[2022-08-07 11:07:33] app.DEBUG [N/A] [6ac3840] [N/A] [Eccube\Log\Logger:log:68] - Transaction is not active. Rollback skipped. [] [GET, /*/store/plugin, **.**.**.**, https://****/store/plugin, Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/104.0.0.0 Safari/537.36]
[2022-08-07 11:07:38] php.INFO [N/A] [9ee992e] [N/A] [Symfony\Component\Debug\ErrorHandler:handleError:532] - User Deprecated: The "sensio_framework_extra.routing.loader.annot_class" service is deprecated since version 5.2 {"exception":"[object] (ErrorException(code: 0): User Deprecated: The \"sensio_framework_extra.routing.loader.annot_class\" service is deprecated since version 5.2 at /var/www/html/ec-cube/var/cache/prod/ContainerO7xxvyx/getSensioFrameworkExtra_Routing_Loader_AnnotClassService.php:8)"} [GET, /, **.**.**.**, NULL, ELB-HealthChecker/2.0]
[2022-08-07 11:07:38] php.INFO [N/A] [9ee992e] [N/A] [Symfony\Component\Debug\ErrorHandler:handleError:532] - User Deprecated: The "Sensio\Bundle\FrameworkExtraBundle\Routing\AnnotatedRouteControllerLoader" class is deprecated since version 5.2. Use "Symfony\Bundle\FrameworkBundle\Routing\AnnotatedRouteControllerLoader" instead. {"exception":"[object] (ErrorException(code: 0): User Deprecated: The \"Sensio\\Bundle\\FrameworkExtraBundle\\Routing\\AnnotatedRouteControllerLoader\" class is deprecated since version 5.2. Use \"Symfony\\Bundle\\FrameworkBundle\\Routing\\AnnotatedRouteControllerLoader\" instead. at /var/www/html/ec-cube/vendor/sensio/framework-extra-bundle/Routing/AnnotatedRouteControllerLoader.php:19)"} [GET, /, **.**.**.**, NULL, ELB-HealthChecker/2.0]
[2022-08-07 11:07:38] php.INFO [N/A] [9ee992e] [N/A] [Symfony\Component\Debug\ErrorHandler:handleError:532] - User Deprecated: The "sensio_framework_extra.routing.loader.annot_dir" service is deprecated since version 5.2 {"exception":"[object] (ErrorException(code: 0): User Deprecated: The \"sensio_framework_extra.routing.loader.annot_dir\" service is deprecated since version 5.2 at /var/www/html/ec-cube/var/cache/prod/ContainerO7xxvyx/getSensioFrameworkExtra_Routing_Loader_AnnotDirService.php:8)"} [GET, /, **.**.**.**, NULL, ELB-HealthChecker/2.0]
[2022-08-07 11:07:38] php.INFO [N/A] [9ee992e] [N/A] [Symfony\Component\Debug\ErrorHandler:handleError:532] - User Deprecated: The "sensio_framework_extra.routing.loader.annot_file" service is deprecated since version 5.2 {"exception":"[object] (ErrorException(code: 0): User Deprecated: The \"sensio_framework_extra.routing.loader.annot_file\" service is deprecated since version 5.2 at /var/www/html/ec-cube/var/cache/prod/ContainerO7xxvyx/getSensioFrameworkExtra_Routing_Loader_AnnotFileService.php:8)"} [GET, /, **.**.**.**, NULL, ELB-HealthChecker/2.0]
[2022-08-07 11:07:38] php.INFO [N/A] [9ee992e] [N/A] [Symfony\Component\Debug\ErrorHandler:handleError:532] - User Deprecated: The "Sensio\Bundle\FrameworkExtraBundle\Configuration\Route" annotation is deprecated since version 5.2. Use "Symfony\Component\Routing\Annotation\Route" instead. {"exception":"[object] (ErrorException(code: 0): User Deprecated: The \"Sensio\\Bundle\\FrameworkExtraBundle\\Configuration\\Route\" annotation is deprecated since version 5.2. Use \"Symfony\\Component\\Routing\\Annotation\\Route\" instead. at /var/www/html/ec-cube/vendor/sensio/framework-extra-bundle/Configuration/Route.php:16)"} [GET, /, **.**.**.**, NULL, ELB-HealthChecker/2.0]