[Feature Request] Option to display/search for just system packges or Flatpak packages

[mdpenguin]

It would be helpful to be able to only see apps that use the type of packaging that users prefer (i.e. deb or Flatpak).

For example, I only keep Flatpak for GIMP and generally stick to deb files or compile apps on my own to avoid the overhead of using containers so I don't want to see Flatpaks when I'm searching or browsing for apps. I know a number of other people like the sandboxing features of Flatpak and try to only use containerized apps, so the ability to only show Flatpaks would be helpful for them.