Discover without administrating the system repos?

On debian/ubuntu based systems (and others like fedora have something similar) I prefer to use synaptic which I find better than discover or gnome-software for maintaining package updates. I don’t mind using discover for flatpak or snaps, but I can’t find out how to tell it to ignore the system repos. Any help please?

To clarify further what my problem is, that both appstream for native packages and packagekit give me a completely inferior experience to using synaptic. On debian, I search for “firefox” and only get the flatpak result, I search for “firefox-esr” and get no results. I can’t even turn off deb repo management because of packagekit. I really want to use discover for other things, that’s why I’m asking for help.