Is there a way to see whether any one application was installed via Snap, from a PPA, via downloaded deb or from a standard repository?

At the moment, I have Zoom installed on my Focal 20.04 laptop. I'm trying to figure out how I initially installed it, but I have this problem fairly often. Either it's a proprietary app (eg. Slack or Dropbox) and I want to update it, or the app is alerting me that a newer version is available (Keepass) and I want to doublecheck that I installed from a repository and can just wait for the repo to be updated.

If I had to guess, I'd say it's likely that I installed Zoom from a downloaded .deb, but I'm not sure how to check. I don't think I installed Slack from a .deb.

I tried to follow some of the suggestions at How do I find out which repository a package comes from? but the results are ambiguous. For instance there's no apt policy result for Slack:

amanda@rajje:~$ apt policy slack

slack:

  Installed: (none)

  Candidate: 1:0.15.2-9

  Version table:

     1:0.15.2-9 500

        500 http://us.archive.ubuntu.com/ubuntu focal/universe amd64 Packages

        500 http://us.archive.ubuntu.com/ubuntu focal/universe i386 Packages

Presumably because I installed it from Ubuntu Software, so it's a Snap:

If I try apt policy for an app that I know I haven't done any monkeying with I see a list of repositories. Can I assume that this means that I did install from a repository?

amanda@rajje:~$ apt policy emacs

emacs:

  Installed: 1:26.3+1-1ubuntu2

  Candidate: 1:26.3+1-1ubuntu2

  Version table:

 *** 1:26.3+1-1ubuntu2 500

        500 http://us.archive.ubuntu.com/ubuntu focal/universe amd64 Packages

        500 http://us.archive.ubuntu.com/ubuntu focal/universe i386 Packages

        100 /var/lib/dpkg/status

And if no repository is shown, does that mean that I installed from a package download?

amanda@rajje:~$ apt policy zoom

zoom:

  Installed: 5.0.403652.0509

  Candidate: 5.0.403652.0509

  Version table:

 *** 5.0.403652.0509 100

        100 /var/lib/dpkg/status