Comment 3 for bug 1864307

There are two things which could be the cause for this:
 1) The appstream-generator used for Focal is old, and there were quite a few fixes to find more icons and ignore apps without sufficient icon data in more recent releases. @laney will hopefully update the tool ;-)

 2) GNOME Software has a bug which makes it always load stock icons for applications, even if they are actually not available on the system and GS should fall back to the cached icons. We've seen this in Debian but I haven't had the time yet to investigate this further.