Create a `systemd` service and add this to the `[Service]` section:

`[Service]`

`Exec=gnome-session-quit --logout --no-prompt`

[How to start a systemd service after user login and stop it before user logout][1]

[How create a service in linux that can handle queries?][2]

[ gnome-session-quit][3]

*Or you can also try the following, which probably won't work:*.

> @reboot sleep 60 && gnome-session-quit --logout --no-prompt
> This might help to wait 60 sec, if the session isn't fully loaded when the system starts, and the logout command might not work immediately for that reason.


 [1]: https://superuser.com/q/1037466/1780440
 [2]: https://unix.stackexchange.com/q/603820/342980
 [3]: https://manpages.ubuntu.com/manpages/focal/en/man1/gnome-session-quit.1.html