After trying to change the default icon set in Elementary OS, I was not able to log in again into the desktop. This happened to me after installing the Qogir-icon-theme. After trying to restore to the default values changing at /etc/lightdm/lightdm.conf and /etc/lightdm/io.elementary.greeter.conf, the only thing that restored the graphical login was the following:
1. On the login screen, press Ctrl + Alt + F1 or Ctrl + Alt + F2 to open a virtual console.
2. Remove elementary-tweaks:
sudo apt purge elementary-tweaks3. Remove all icon related folders at /usr/share/icons and ~/.local/share/icons
4. Reboot and hopefully, you will be able to login again in graphic mode.
5. The icons might not be the ‘elementary’ default set. So to fix this you will need to install again elementary-tweaks and configure it:
sudo apt install elementary-tweaks