GNOME Shell extensions have a UUID property; this key lists extensions which should be disabled, even if loaded as part of the current mode. You can also manipulate this list with the EnableExtension and DisableExtension D-Bus methods on org.gnome.Shell. This key takes precedence over the “enabled-extensions” setting.
This key overrides the automatic hiding of the “Log out” action in the system menu for logged-in situations where there is a single, local, non-system user and only a single available session type (e.g. GNOME on Wayland).