/usr/include/KF5/WebEngineViewer/ is in libkf5webengineviewer-dev 4:17.12.3-0ubuntu3.
This file is owned by root:root, with mode 0o755.
..
/usr/include/KF5/WebEngineViewer/CheckPhishingUrlCache
/usr/include/KF5/WebEngineViewer/CheckPhishingUrlJob
/usr/include/KF5/WebEngineViewer/CheckPhishingUrlUtil
/usr/include/KF5/WebEngineViewer/CreatePhishingUrlDataBaseJob
/usr/include/KF5/WebEngineViewer/FindBarBase
/usr/include/KF5/WebEngineViewer/FindBarWebEngineView
/usr/include/KF5/WebEngineViewer/HashCacheManager
/usr/include/KF5/WebEngineViewer/InterceptorManager
/usr/include/KF5/WebEngineViewer/LocalDataBaseManager
/usr/include/KF5/WebEngineViewer/NetworkPluginUrlInterceptor
/usr/include/KF5/WebEngineViewer/NetworkPluginUrlInterceptorConfigureWidget
/usr/include/KF5/WebEngineViewer/NetworkPluginUrlInterceptorInterface
/usr/include/KF5/WebEngineViewer/NetworkUrlInterceptor
/usr/include/KF5/WebEngineViewer/NetworkUrlInterceptorPluginManager
/usr/include/KF5/WebEngineViewer/SearchFullHashJob
/usr/include/KF5/WebEngineViewer/UpdateDataBaseInfo
/usr/include/KF5/WebEngineViewer/WebEngineAccessKey
/usr/include/KF5/WebEngineViewer/WebEngineExportHtmlPageJob
/usr/include/KF5/WebEngineViewer/WebEngineManageScript
/usr/include/KF5/WebEngineViewer/WebEnginePage
/usr/include/KF5/WebEngineViewer/WebEngineScript
/usr/include/KF5/WebEngineViewer/WebEngineView
/usr/include/KF5/WebEngineViewer/WebHitTest
/usr/include/KF5/WebEngineViewer/WebHitTestResult
/usr/include/KF5/WebEngineViewer/ZoomActionMenu