/usr/share/plasma/plasmoids/org.kde.plasma.userswitcher/ is in plasma-widgets-addons 4:5.12.4-0ubuntu1.
This file is owned by root:root, with mode 0o755.
..
/usr/share/plasma/plasmoids/org.kde.plasma.userswitcher/contents/
/usr/share/plasma/plasmoids/org.kde.plasma.userswitcher/contents/config/
/usr/share/plasma/plasmoids/org.kde.plasma.userswitcher/contents/config/config.qml
/usr/share/plasma/plasmoids/org.kde.plasma.userswitcher/contents/config/main.xml
/usr/share/plasma/plasmoids/org.kde.plasma.userswitcher/contents/ui/
/usr/share/plasma/plasmoids/org.kde.plasma.userswitcher/contents/ui/ListDelegate.qml
/usr/share/plasma/plasmoids/org.kde.plasma.userswitcher/contents/ui/configGeneral.qml
/usr/share/plasma/plasmoids/org.kde.plasma.userswitcher/contents/ui/main.qml
/usr/share/plasma/plasmoids/org.kde.plasma.userswitcher/metadata.desktop
/usr/share/plasma/plasmoids/org.kde.plasma.userswitcher/metadata.json