as expected, fwupd.service was not the cause here for the shutdown delay.
much more likely, these lines give the hint for the real problem:
>[ 281.183873] systemd[1722]: gnome-session-manager@gnome.service: State 'stop-final-sigterm' timed out. Killing.
>[ 281.192441] systemd[1722]: gnome-session-manager@gnome.service: Killing process 2022 (tracker-miner-f) with signal SIGKILL.
>[ 281.194352] systemd[1722]: gnome-session-manager@gnome.service: Killing process 2108 (gmain) with signal SIGKILL.
>[ 281.196221] systemd[1722]: gnome-session-manager@gnome.service: Killing process 2180 (gdbus) with signal SIGKILL.
>[ 281.198033] systemd[1722]: gnome-session-manager@gnome.service: Killing process 2181 (dconf worker) with signal SIGKILL.
>[ 281.199863] systemd[1722]: gnome-session-manager@gnome.service: Killing process 2272 (pool-tracker-mi) with signal SIGKILL.
>[ 281.218395] systemd[1722]: gnome-session-manager@gnome.service: Failed with result 'timeout'.
>[ 281.219724] systemd[1722]: Stopped GNOME Session Manager (session: gnome).
Seeing that this issue only happens on upgrades, I highly suspect tracker to be
involved; from the gnome-music test run we already know that the tracker
database was not properly converted and is corrupt. This can well lead to those
shutdown issues as well.