Would it be possible to add "repositories" from cross-platform offers? Is this a wrong place to post, I'd much rather post in a bug tracker for discover. Some that I know are flatpak, snapd, nix (doesn't work terribly well in terms of compatibilty or stable releases supposedly).

There're a bunch of backends without instrucitons: https://github.com/KDE/discover/tree/ma ... r/backends
for flatpack after installing itself and the backend I also had to add the actual official "ppa", so don't expect that simply adding related libraries will just enable support.

the flatpack, snapd and packagekit can be installed with discover itself and handles everything. search for "discover backend".