/usr/share/kwin/tabbox/ is in kwin-addons 4:5.5.5-0ubuntu1.
This file is owned by root:root, with mode 0o755.
..
/usr/share/kwin/tabbox/big_icons/
/usr/share/kwin/tabbox/big_icons/contents/
/usr/share/kwin/tabbox/big_icons/contents/ui/
/usr/share/kwin/tabbox/big_icons/contents/ui/IconTabBox.qml
/usr/share/kwin/tabbox/big_icons/contents/ui/main.qml
/usr/share/kwin/tabbox/big_icons/metadata.desktop
/usr/share/kwin/tabbox/compact/
/usr/share/kwin/tabbox/compact/contents/
/usr/share/kwin/tabbox/compact/contents/ui/
/usr/share/kwin/tabbox/compact/contents/ui/main.qml
/usr/share/kwin/tabbox/compact/metadata.desktop
/usr/share/kwin/tabbox/informative/
/usr/share/kwin/tabbox/informative/contents/
/usr/share/kwin/tabbox/informative/contents/ui/
/usr/share/kwin/tabbox/informative/contents/ui/main.qml
/usr/share/kwin/tabbox/informative/metadata.desktop
/usr/share/kwin/tabbox/present_windows/
/usr/share/kwin/tabbox/present_windows/contents/
/usr/share/kwin/tabbox/present_windows/contents/ui/
/usr/share/kwin/tabbox/present_windows/contents/ui/main.qml
/usr/share/kwin/tabbox/present_windows/metadata.desktop
/usr/share/kwin/tabbox/small_icons/
/usr/share/kwin/tabbox/small_icons/contents/
/usr/share/kwin/tabbox/small_icons/contents/ui/
/usr/share/kwin/tabbox/small_icons/contents/ui/IconTabBox.qml
/usr/share/kwin/tabbox/small_icons/contents/ui/main.qml
/usr/share/kwin/tabbox/small_icons/metadata.desktop
/usr/share/kwin/tabbox/text/
/usr/share/kwin/tabbox/text/contents/
/usr/share/kwin/tabbox/text/contents/ui/
/usr/share/kwin/tabbox/text/contents/ui/main.qml
/usr/share/kwin/tabbox/text/metadata.desktop
/usr/share/kwin/tabbox/thumbnails/
/usr/share/kwin/tabbox/thumbnails/contents/
/usr/share/kwin/tabbox/thumbnails/contents/ui/
/usr/share/kwin/tabbox/thumbnails/contents/ui/main.qml
/usr/share/kwin/tabbox/thumbnails/metadata.desktop