Solved it by removing the local cache of GNOME Software and forcing it to re-download its data
$ killall gnome-software $ rm -r ~/.local/share/gnome-software
... et voilà, Thunderbird magically appeared in the software catalogue.
Solved it by removing the local cache of GNOME Software and forcing it to re-download its data
$ killall gnome-software share/gnome- software
$ rm -r ~/.local/
... et voilà, Thunderbird magically appeared in the software catalogue.