/usr/share/gnome-shell/extensions/ is in gnome-shell-extension-onboard 1.4.1-2ubuntu1.
This file is owned by root:root, with mode 0o755.
..
/usr/share/gnome-shell/extensions/Onboard_Indicator@onboard.org/
/usr/share/gnome-shell/extensions/Onboard_Indicator@onboard.org/convenience.js
/usr/share/gnome-shell/extensions/Onboard_Indicator@onboard.org/extension.js
/usr/share/gnome-shell/extensions/Onboard_Indicator@onboard.org/metadata.json
/usr/share/gnome-shell/extensions/Onboard_Indicator@onboard.org/prefs.js
/usr/share/gnome-shell/extensions/Onboard_Indicator@onboard.org/schemas/
/usr/share/gnome-shell/extensions/Onboard_Indicator@onboard.org/schemas/gschemas.compiled
/usr/share/gnome-shell/extensions/Onboard_Indicator@onboard.org/schemas/org.gnome.shell.extensions.onboard-indicator.gschema.xml
/usr/share/gnome-shell/extensions/Onboard_Indicator@onboard.org/stylesheet.css