I’ve read the specification in https://wiki.archlinux.org/title/XDG_Autostart
but it does not help either:
purism@pureos:~$ diff ~/.config/xdg/autostart/gnome-software-service.desktop /etc/xdg/autostart/gnome-software-service.desktop
8,10d7
< # see: https://forums.puri.sm/t/packagekitd-what-it-is-doing/20527/8
< X-GNOME-Autostart-enabled=false
< Hidden=true
purism@pureos:~$ ps ax | grep gnome-soft
1552 tty7 Sl+ 0:10 /usr/bin/gnome-software --gapplication-service
Aaaaah, sorry, my fault - the correct path is ~/.config/autostart/ 
Thanks! This dit it:
purism@pureos:~$ diff ~/.config/autostart/gnome-software-service.desktop /etc/xdg/autostart/gnome-software-service.desktop
8,10d7
< # see: https://forums.puri.sm/t/packagekitd-what-it-is-doing/20527/8
< X-GNOME-Autostart-enabled=false
< Hidden=true
purism@pureos:~$ ps ax | grep gnome-soft
The issue is still not finally solved as packagekitd gets also started via dbus:
purism@pureos:~$ sudo grep packagekit /var/log/syslog | grep 'Jun 13 09'
Jun 13 09:37:07 pureos dbus-daemon[536]: [system] Activating via systemd: service name='org.freedesktop.PackageKit' unit='packagekit.service' requested by ':1.153' (uid=0 pid=3130 comm="/usr/bin/gdbus call --system --dest org.freedeskto")
For it to get started by dbus, something needs to actively request it. That “something” usually is GNOME Software/PureOS Store.
In your case, looks like it was some script running as PID 3130?
The proc wasn’t visible anymore. Is it possible to higher the loglevel of the dbus-daemon because nothing can be found in any log files either.
I tried to monitor the dbus-daemon with:
sudo dbus-monitor --system 'destination=org.freedesktop.PackageKit' 'sender=org.freedesktop.PackageKit'
which produces some output but maybe not the correct one; the problem must be solved for the L5 because the running daemon is highly CPU (read: battery) consuming, in 12 hours:
purism@pureos:~$ ps ax | grep pack
12283 ? Ssl 3:18 /usr/libexec/packagekitd