The firmware updates here do not come from your distro’s software archive, but from lvfs, via the fwupdmgr tool for the purpose, not dnf.
Now, I do not see your normal Fedora RPM repos showing, but that may just be a UI issue, assuming that your screenshot is capturing the whole window.
Sometimes Discover is very slow to load or show all the software sources when it is fetching and possibly installing updates in the background, especially when it has to check for updates from five or six different sources. i.e Snap, Firmware, KDE Store, Fedora Flatpak, Flathub flatpak, and the standard repos.
1. Thanks for the clarifications, I miss the knowledge on a vocabulary - infrastructural standpoint for what concerns fedora and KDE
2. I confirm that the screenshot is not cut.
3. Point is that with dnf, anyway, I receive results that are not showing in Discover: but as you stated, they may appear anyway in a couple of days, because it’s slow. Correct?
4. Is there a way to check that the normal fedora RPM repos are there? Even if I do not see them in a potential UI issue?
5. I have tried a fwupdmgr update and it seems that everything is up to date
The doubt actually raised from the fact that before I received updates almost everyday. Now with snap enabled, not anymore.
If dnf is working, that should be enough, I’d think.
I’m not running before anywhere currently, so I can’t say for sure, but I wonder if this isn’t a bug. This happens on the Kubuntu LTS release, and maybe 25.04 after a change in the format for source files in Apt.
There could be a bug of some sort in the dnf plugin that Discover uses, maybe.