Before shutting down, I ran sudo dnf update and got the message "Nothing to do", indicating that all packages are already up-to-date.
However, when I selected Power Off in the GNOME interface, I received the following response:
This message seems to indicate that there are still packages that need to be updated, and they will be updated during the shutdown process. How can I find out which packages will be updated? Because sudo dnf update didn’t show any packages that needed updating.
There is a difference on how/when dnf and GNOME Software are automatically refreshing their metadata. This is probably the cause of the difference, given that it seems you have run sudo dnf upgrade without the --refresh argument, if I’m not mistaken. You might want to check for Flatpak updates too.
IIRC, I have also seen a particular situation when GNOME Software, having its metadata refreshed and packages downloaded for update (the setting to Automatically check for and download updates enabled), but the user runs the updates with dnf, yet GNOME Software doesn’t “pick up” this action and considers there are still packages to be installed.
In your particular case, you could open GNOME Software to see what would be the packages suggested for upgrade.
I usually suggest choosing only one tool for the updates (either GNOME Software, or dnf upgrade + flatpak update with automatic updates in GNOME Software disabled).
