Snap-store app shows some non-snap apps but not others

Why does the snap-store app (Ubuntu Software) show programs that are not snaps? For example, deja-dup (/etc/bin/deja-dup or aka backups) is not a snap but shows in snap-store.

Conversely, snap-store does not show other non-snap software that has been installed.

So why does it show some installed software and not others? I am under the impression that snap-store handles snap packages only, but this does not appear to be the case.

I am running Ubuntu 20.04 LTS Gnome.

The snap-store has always handled .deb and .snap packages …

Thanks but why does it not show all packages that are installed? I gave backups as just one example but there are many more.

Perhaps I should say that I also use Synaptic Package Manager (SPM). So perhaps SPM and snap store do not play well together.

Both use the dpkg database from disk and should not have any influence on each other … are you sure the deja-dup you see is not the snap ? IIRC in the old gnome-software based snap-store it is not as easy to tell apart snaps and deps (the new snap-store that does not base on gnome-software (from the preview/candidate channel) makes such stuff way clearer …) … the snap based deja-dup is most likely a lot newer than the deb which might cause gnome-software/snap-store to offer it to you …

Oops I made a mistake. backup (deja-dup) is NOT a good example of an installed package that does not show up as being installed in the snap store app. It’s an example of a non-snap being listed in the snap store app. Also, backup was already pre-installed when I got this new laptop.

I’m assuming that backup is not a snap because when I do a “which deja-dup” I get /usr/bin/deja-dup, which according to my understanding is not a snap. Also when I do a “snap list --all” command it does not show.

Anyway, back to my original concern, which is that there seems to be some inconsistency between what is actually installed and what is listed as installed in the snap store app. I haven’t done a thorough analysis - this is just based on casual observation over time. Note that I install most S/W via Synaptic Package Manager because I just came from another version of Linux where I used SPM and snap wasn’t used. In fact I never heard of snap until I switched to Ubuntu.

So essentially it is confusing to install something via SPM and not see it listed as installed in the snap store app, and I’m trying to get a clearer picture of what is going on here.