If you are not able to use the keyboard only on the desktop screen and it works perfectly fine everywhere else, then it is probably because of the bug with the gnome desktop icons. If this case is applicable to you, it is evident that your system is not up-to-date and needs to be updated as this bug has been fixed. To update your system, do the following:
1. First of all, open up a Terminal window.
2. After that, enter the following command to update the packages database:
$ sudo apt update
3. Once this command has run successfully, enter the following command to initiate the upgrade:
$ sudo apt upgrade
4. When prompted, type Y to start the upgrade. Wait for it to complete.
5. Once it has completed, reboot your system and see if the issue is fixed.
In case the issue is still not fixed, what you can do is install different desktop icons and uninstall the gnome-desktop-icons for the time being. To remove the gnome desktop icons package, use the sudo apt purge gnome-desktop-icons command. Once removed, you can install another file manager and you’ll be good to go.