More and more apps are available only as snaps. For example, chromium is available only as snap from 19.10 onwards. But there are other more or less useful snaps such as anbox.
Unfortunately, the panel in Lubuntu does not list the snaps in the application menu.
The *.desktop files of snaps are located in /var/lib/snapd/desktop/applications. I guess, that the panel is not looking for them, because the path is not specified.
Fix it for Lubuntu 20.04.
Evaluate, if this can and should be SRUed to 19.10.