Unfortunately, there is no easy way to add an an icon from the Application overview to your desktop. Instead, you need to find the .desktop file of the application and copy it over to your "Desktop" folder. These text files with a .desktop extension will usually be in either /usr/share/applications, for applications installed using APT (".deb packages"), or in /var/lib/snapd/desktop/applications, for snap packages.
Background
The workflow of having application icons on your desktop, such as it was when Windows 95 appeared in 1995, has been kind of deprecated by the Gnome Shell developpers.
- These icons are not accessible while you work: your windows will cover them.
- It can involve a security risk if any user, or perhaps malware, can place any executable on the desktop
In principle, application icons are installed from trusted sources by your system administrator (that will likely be yourself on your own computer). Conventional installers will automatically install a launcher in dedicated places, from where they are picked up in the application menu.
- It takes hitting Super then typing a few letters to launch any of the installed applications
- If you use the application quite regularly, drag it to the first page in the Application Overview, where you will see it immediately when you open that view (Shortcut key: Super+a).
- If you use it very frequently, place it on the Dock as a favourite (right-click the icon, select "Add to favorites" and optionally drag the icon on the desired place on the dock). You have one-click access, even while you are working (i.e., other windows are open). You can also access these applications with a single shortcut key, i.e., Super+1 for the left most application on the dock, etc.
That said about Gnome Desktop, Ubuntu reintroduced support for Desktop icons through a dedicated Gnome Shell extension. That is mainly intended to host your current user files, however, you can also place application launchers there by copying .desktop files to the Desktop folder.
