/usr/include/KF5/CalendarSupport/ is in libkf5calendarsupport-dev 4:17.12.3-0ubuntu1.
This file is owned by root:root, with mode 0o755.
..
/usr/include/KF5/CalendarSupport/ArchiveDialog
/usr/include/KF5/CalendarSupport/CalPrintDefaultPlugins
/usr/include/KF5/CalendarSupport/CalPrintPluginBase
/usr/include/KF5/CalendarSupport/CalPrinter
/usr/include/KF5/CalendarSupport/CalendarSingleton
/usr/include/KF5/CalendarSupport/CategoryConfig
/usr/include/KF5/CalendarSupport/CategoryHierarchyReader
/usr/include/KF5/CalendarSupport/CellItem
/usr/include/KF5/CalendarSupport/CollectionSelection
/usr/include/KF5/CalendarSupport/EventArchiver
/usr/include/KF5/CalendarSupport/FreeBusyCalendar
/usr/include/KF5/CalendarSupport/FreeBusyItem
/usr/include/KF5/CalendarSupport/FreeBusyItemModel
/usr/include/KF5/CalendarSupport/FreePeriodModel
/usr/include/KF5/CalendarSupport/IdentityManager
/usr/include/KF5/CalendarSupport/IncidenceViewer
/usr/include/KF5/CalendarSupport/KCalPrefs
/usr/include/KF5/CalendarSupport/MessageWidget
/usr/include/KF5/CalendarSupport/Plugin
/usr/include/KF5/CalendarSupport/PrintPlugin
/usr/include/KF5/CalendarSupport/Utils