Ubuntu 20.04 desktop files and icons missing

This worked for me:

• Install gnome-shell-extension-desktop-icons:

sudo apt install gnome-shell-extension-desktop-icons

• Log out of Gnome.
• Log back in.

The problem might be that the installation did not go according to plans, not to worry though! The simplest (and most effective) operation you can do is:

sudo apt dist-upgrade

This will automatically install / update / repair all the needed packages for your current version.