I've found remains of mate, removed it:
$ sudo apt remove -y ubuntu-mate-desktop mate-* ubuntu-mate-* \
plymouth-theme-ubuntu-mate-* lightdm
$ sudo apt autoremove -y
$ sudo apt install --reinstall -y gdm3
$ sudo reboot
Now everything works just fine. Please, close this bug.
--
You
Public bug reported:
Double clicking on any folder located on the Desktop or even right click
and then Open, does nothing.
System and package info:
Description:Ubuntu 18.04.1 LTS
Release:18.04
nautilus:
Installed: 1:3.26.4-0~ubuntu18.04.1
Candidate: 1:3.26.4-0~ubuntu18.04.1
