Experimenting with user-services & desktop notifications failure

Edit: HOLD THE FRONT DOOR! I’m on Ubuntu Mate. I had completely forgotten about this bug which I filed about notifications on Ubuntu Mate being broken for all snaps!

I’m experimenting with user services configured as below:

    command: bin/accomplishments-daemon
    extensions: [flutter-beta]
    daemon: simple
      daemon-scope: user
      - accomplishments-service # the dbus service
      - gsettings
      - hardware-observe
      - home
      - log-observe
      - network

The flutter extension adds the desktop plug which AFAICT should be enough to allow notification messages sent via dbus to org.freedesktop.Notifications, method Notify. However it seems that my user daemon is being denied via apparmor:

Nov 19 02:50:31 cerritos dbus-daemon[1156855]: apparmor="DENIED" operation="dbus_method_call"  bus="session" path="/org/freedesktop/Notifications" interface="org.freedesktop.Notifications" member="Notify" mask="send" name="org.freedesktop.Notifications" pid=1832629 label="snap.ubuntu-accomplishments.daemon"

The library I’m using to trigger desktop notifications is the Canonical-developed desktop_notifications.dart package for Dart apps:

Any clue whether this is a bug or are user daemons not allowed to send desktop notifications on purpose?

btw, there were previous discussions about this