Open the tool "Extensions", which, if not installed, can be installed with the command sudo apt install gnome-shell-extension-prefs. Under "Build-in", enable "Desktop Icons NG (DING)". (This can also be done with Extension Manager, package: gnome-shell-extension-manager).

If that extension is not listed, then likely components of the standard Ubuntu desktop have been removed. Check whether either ubuntu-desktop or ubuntu-desktop-minimal are installed. If not, then install one of the two with the terminal command (for example for minimal): sudo apt install ubuntu-desktop-minimal.

If one of these packages are effectively installed, then something must be broken on your system. Then you can try explicitly reinstalling the Desktop icons extension: sudo apt install --reinstall gnome-shell-extension-ubuntu-dock.