I’ve recently added the AppStream metainfo file to an editor called Frescobaldi. This file is available in Fedora 32 since version 3.1.2-2.
This editor cannot be found in GNOME Software. I hoped that adding the metainfo file would have fixed this but it didn’t.
IIUC (but I may be wrong) GNOME Software relies on the metadata generated by the distro with appstream-builder and distributed by the package appstream-data. But this package has not been updated for a month. I would expect metadata to be rebuilt if needed, or at least more often.
According to this message, metadata are built weekly. But it doesn’t seem true.
AFAIK this package is only used on installation media, so that users can see package metadata in gnome-software and such even when offline.
Generating the metadata and incorporating them in the repository files is rather costly and I don’t know if it happens weekly or if Richard keeps on doing it manually. Better ask on devel.
if it is, then it should be included in gnome-software when the appstream-data is generated the next time: this is after the package hits stable, I don’t think packages in updates-testing are included in the appdata generation.
if both of these steps are correct, and it still doesn’t show, best to file a bug so that it can be debugged.
The release notes do not show weekly updates, that’s true. But the description says “The appstream data is built weekly with /usr/bin/appstream-builder…”, see here.
The doc page you linked makes a distinction between appdata.xml file for GUI apps and metainfo.xml file for add-ons. This doesn’t match current AppStream specification AFAICS. As you can read here and also here, appdata.xml name is still supported for historical reasons but it’s kind of deprecated.
I’ve opened an issue four months ago, but nobody replied so far.
For Frescobaldi (a GUI app) I’ve used only a metainfo.xml file. Is this a problem?
appstreamcli search frescobaldi was immediately able to find the application, as soon as the metainfo.xml file reached stable a few days ago.
So my feeling is that the problem is either the out-of-date appstream-data or GNOME Software.
If you want to debug it yourself, install the package:
sudo dnf install frescobaldi
(it will install a lot of dependencies though, as it depends on lilypond, which depends on texlive)