FlightGear has no working appdata. This package does show up in software and right click show details has no details for FlightGear.
FEDORA-2019-2246acf4c1 has been submitted as an update to Fedora 31. https://bodhi.fedoraproject.org/updates/FEDORA-2019-2246acf4c1
Thank you for reporting this problem. The builtin appdata file should be fixed now. It now passes the appstream-util validate command successfully. FlightGear should show up back in gnome-software when the appstream-data package will be updated. It picks up a compilation of all appdata files in fedora-31.xml.gz from upstream, and from what I observed, gnome-software uses this file locally to display available software.
FlightGear-2019.1.1-3.fc31 has been pushed to the Fedora 31 stable repository. If problems still persist, please make note of it in this bug report.