I leverage a couple of packages as part of an initiative called XtraDeb. After adding the associated PPA repositories, it is possible to install the packages via apt (e.g. "sudo apt install gzdoom"). Unfortunately, none of these new packages show up in gnome-software.
The behavior is consistent with all third-party repositories I have tested (and also packages such as openssh-server). It looks like gnome-software filters out non official distribution packages (and some ?!? non GUI ?!?).
To the extent of my knowledge, this issue exists for a very long time in every Ubuntu version. For the sake of the exercise, let's say since Ubuntu Focal. This problem is already reported here https://bugs.launchpad.net/ubuntu/+source/gnome-software/+bug/1818990 and here https://gitlab.gnome.org/GNOME/gnome-software/-/issues/1971.
To provide just a bit more background, I usually install gnome-software with "sudo apt install gnome-software" (after removing the Ubuntu Software snap). I also packaged, installed and tested the latest version with and without the distribution patches.
From what I was told, gnome-software uses packagekit to retrieve the packages and I confirm PPA packages are searchable there. For instance, pkcon get-details <xtradeb package> finds the package. Still, this package doesn't show in gnome-software.
I also set this without any observable outcome:
gsettings set org.gnome.software free-repos "['ubuntu-*-main', 'ubuntu-*-universe', 'lp_ppa_xtradeb_*-*-main']"
Anyone has any idea on how to overcome this issue or some insight on how to debug it?
