/usr/share/plasma/wallpapers/ is in plasma-wallpapers-addons 4:5.12.4-0ubuntu1.
This file is owned by root:root, with mode 0o755.
..
/usr/share/plasma/wallpapers/org.kde.haenau/
/usr/share/plasma/wallpapers/org.kde.haenau/contents/
/usr/share/plasma/wallpapers/org.kde.haenau/contents/ui/
/usr/share/plasma/wallpapers/org.kde.haenau/contents/ui/BackgroundElement.qml
/usr/share/plasma/wallpapers/org.kde.haenau/contents/ui/BottomBackgroundElement.qml
/usr/share/plasma/wallpapers/org.kde.haenau/contents/ui/RightBackgroundElement.qml
/usr/share/plasma/wallpapers/org.kde.haenau/contents/ui/main.qml
/usr/share/plasma/wallpapers/org.kde.haenau/contents/ui/wallpaper.svgz
/usr/share/plasma/wallpapers/org.kde.haenau/metadata.desktop
/usr/share/plasma/wallpapers/org.kde.haenau/metadata.json
/usr/share/plasma/wallpapers/org.kde.hunyango/
/usr/share/plasma/wallpapers/org.kde.hunyango/contents/
/usr/share/plasma/wallpapers/org.kde.hunyango/contents/ui/
/usr/share/plasma/wallpapers/org.kde.hunyango/contents/ui/main.qml
/usr/share/plasma/wallpapers/org.kde.hunyango/contents/ui/wallpaper.svgz
/usr/share/plasma/wallpapers/org.kde.hunyango/metadata.desktop
/usr/share/plasma/wallpapers/org.kde.hunyango/metadata.json
/usr/share/plasma/wallpapers/org.kde.potd/
/usr/share/plasma/wallpapers/org.kde.potd/contents/
/usr/share/plasma/wallpapers/org.kde.potd/contents/config/
/usr/share/plasma/wallpapers/org.kde.potd/contents/config/main.xml
/usr/share/plasma/wallpapers/org.kde.potd/contents/ui/
/usr/share/plasma/wallpapers/org.kde.potd/contents/ui/config.qml
/usr/share/plasma/wallpapers/org.kde.potd/contents/ui/main.qml
/usr/share/plasma/wallpapers/org.kde.potd/metadata.desktop
/usr/share/plasma/wallpapers/org.kde.potd/metadata.json