The installed section does not display any package installed via deb or ppa Reproducible: Always
Only application packages will be shown, which is defined by whether application metadata is provided, offered by appstream.
Will it be kept this way? Because this will make it hard to uninstall said deb-sourced and ppa-sourced packages
Appstream has plans to support such cases. Will wait for their feedback.
Implemented upstream, integrated in future Discover 5.9.