No Application found in Ubuntu Software Center 20.04

It boils down to an issue between the apt and snap versions of Ubuntu Software.

This answer from an earlier question helped to provide a solution.

What I did

In terminal:

snap remove snap-store  
sudo apt-get install gnome-software

followed by

sudo apt install gnome-software-plugin-snap

That installed Software as opposed to the large yellow icon previously associated with Ubuntu Software after which the "missing" packages were then correctly listed.

There are solutions to restore the old icon if I wish (not essential) and to reinstall snap-store which can apparently co-exist with the apt version