Install xfce4-session by entering the following commands in the terminal:
sudo apt update sudo apt install xfce4-session
Description:
Xfce4 Session Manager
xfce4-session is an X11-compliant "session manager" designed for use with the Xfce4 Desktop Environment. On log out, the session manager saves the state of all your running applications. When you log back in, the session manager restores the same applications with the same window positions.
Homepage: http://www.xfce.org/
Version: 4.12.1-3ubuntu3
Section: universe/x11